get_project ignores project config

### Issue

I have a project that I'm attempting to migrate from another editor to vim, and part of what I want to set up is jedi completion and go-to-definition for several nested python projects. I have created a `.jedi/project.json` file in the repository root, that defines `added_sys_path` entries for the sub-projects, as well as some stub files I wrote for third-party code.

When I attempt to jump between sub-projects, jedi cannot find the definitions of classes etc.
This appears to be because the `added_sys_path` entries are not present in the project returned from `get_project`.
The `JediLoadProject` command does load a properly configured project, but under a non-matching key, so `get_project` overwrites it.

It appears that `get_project` creates a `Project` object with the correct `path`, but ignoring the actual data on disk.

I have currently worked around this using the following patch:

```
diff --git a/pythonx/jedi_vim.py b/pythonx/jedi_vim.py
index 70a524c..cf51564 100644
--- a/pythonx/jedi_vim.py
+++ b/pythonx/jedi_vim.py
@@ -232,11 +232,11 @@ def get_project():
environment_path = vim_environment_path

if vim_project_path in ("auto", "", None):
- project_path = jedi.get_default_project().path
+ project = jedi.get_default_project()
else:
- project_path = vim_project_path
+ project = jedi.Project(vim_project_path)

- project = jedi.Project(project_path, environment_path=environment_path)
+ project._environment_path = environment_path

_current_project_cache = cache_key, project
return project
```
This patch gives me the expected behavior noted below, and appears to work correctly in my actual project.
EDIT: On reflection, it probably makes more sense to use `Project.load` in the else branch, but I don't think I hit that, so I left it basically the same.

### Steps to reproduce

1. Create a directory with a `.jedi/project.json` file that contains `[1, {"path": ".", "added_sys_path": ["some/junk"]}]`.
2. In the directory, start vim and run `:pythonx import jedi_vim; print(jedi_vim.get_project().added_sys_path)`.
3. Against master, this prints `[]` instead of `['some/junk']`

### Output of “:verbose JediDebugInfo”

#### Jedi-vim debug information

##### jedi-vim version

- jedi-vim git version: 0.11.0-8-g960eaa8-dirty
- jedi git submodule status: 8ef2ce232cebf6f30b41b28b2677d84666a97d55 pythonx/jedi (v0.18.0-40-g8ef2ce23)
- parso git submodule status: ef90bba3b3d4310c345885a1368dbfc8937765a3 pythonx/parso (v0.8.1-1-gef90bba)

##### Global Python

Using Python version 3 to access Jedi.
- global sys.executable: `/home/maxchase/.pyenv/versions/nvim/bin/python`
- global sys.version: `3.9.1 (default, Dec 31 2020, 10:49:22), [GCC 9.3.0]`
- global site module: `/home/maxchase/.pyenv/versions/3.9.1/lib/python3.9/site.py`

##### Jedi

- path: `/home/maxchase/.local/share/nvim/site/pack/mwchase/start/jedi-vim/pythonx/jedi/jedi/__init__.py`
- version: 0.18.0

##### Jedi environment:

- executable: /home/maxchase/.pyenv/versions/nvim/bin/python
- sys_path:
- `/home/maxchase/.pyenv/versions/3.9.1/lib/python39.zip`
- `/home/maxchase/.pyenv/versions/3.9.1/lib/python3.9`
- `/home/maxchase/.pyenv/versions/3.9.1/lib/python3.9/lib-dynload`
- `/home/maxchase/.pyenv/versions/nvim/lib/python3.9/site-packages`

##### Known environments

- (/usr/bin/python3.8)

##### Settings

```
g:jedi#use_tabs_not_buffers = 1 (default: 0)

omnifunc=jedi#completions
Last set from ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/autoload/jedi.vim line 712
completeopt=menuone,longest,preview
Last set from ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/plugin/jedi.vim line 36
```

#### :version
```

NVIM v0.4.3
Build type: Release
LuaJIT 2.1.0-beta3
Compilation: /usr/bin/cc -g -O2 -fdebug-prefix-map=/build/neovim-gOb7vg/neovim-0.4.3=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=1 -DDISABLE_LOG -Wdate-time -D_FORTIFY_SOURCE=1 -O2 -DNDEBUG -DMIN_LOG_LEVEL=3 -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion -Wmissing-prototypes -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fdiagnostics-color=always -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -I/build/neovim-gOb7vg/neovim-0.4.3/build/config -I/build/neovim-gOb7vg/neovim-0.4.3/src -I/usr/include -I/usr/include/lua5.1 -I/build/neovim-gOb7vg/neovim-0.4.3/build/src/nvim/auto -I/build/neovim-gOb7vg/neovim-0.4.3/build/include
Compiled by team+vim@tracker.debian.org

Features: +acl +iconv +tui
See ":help feature-compile"

system vimrc file: "$VIM/sysinit.vim"
fall-back for $VIM: "/usr/share/nvim"

Run :checkhealth for more info
```

#### :messages
```
```

:scriptnames

```
1: ~/.config/nvim/init.vim
2: /usr/share/nvim/runtime/syntax/syntax.vim
3: /usr/share/nvim/runtime/syntax/synload.vim
4: /usr/share/nvim/runtime/syntax/syncolor.vim
5: /usr/share/nvim/runtime/filetype.vim
6: ~/.local/share/nvim/site/pack/mwchase/start/vim-colors-solarized/colors/solarized.vim
7: /usr/share/nvim/runtime/ftplugin.vim
8: /usr/share/nvim/runtime/indent.vim
9: /usr/share/nvim/runtime/plugin/gzip.vim
10: /usr/share/nvim/runtime/plugin/health.vim
11: /usr/share/nvim/runtime/plugin/man.vim
12: /usr/share/nvim/runtime/plugin/matchit.vim
13: /usr/share/nvim/runtime/pack/dist/opt/matchit/plugin/matchit.vim
14: /usr/share/nvim/runtime/plugin/matchparen.vim
15: /usr/share/nvim/runtime/plugin/netrwPlugin.vim
16: /usr/share/nvim/runtime/plugin/rplugin.vim
17: /usr/share/nvim/runtime/plugin/shada.vim
18: /usr/share/nvim/runtime/plugin/spellfile.vim
19: /usr/share/nvim/runtime/plugin/tarPlugin.vim
20: /usr/share/nvim/runtime/plugin/tohtml.vim
21: /usr/share/nvim/runtime/plugin/tutor.vim
22: /usr/share/nvim/runtime/plugin/zipPlugin.vim
23: ~/.local/share/nvim/site/pack/mwchase/start/black/plugin/black.vim
24: /usr/share/nvim/runtime/autoload/provider/python3.vim
25: /usr/share/nvim/runtime/autoload/provider/pythonx.vim
26: /usr/share/nvim/runtime/autoload/remote/host.vim
27: /usr/share/nvim/runtime/autoload/provider.vim
28: ~/.local/share/nvim/site/pack/mwchase/start/dirsettings/plugin/dirsettings.vim
29: ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/plugin/jedi.vim
30: ~/.local/share/nvim/site/pack/mwchase/start/python-syntax/syntax/python.vim
31: /usr/share/nvim/runtime/syntax/python.vim
32: ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/after/syntax/python.vim
33: ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/autoload/jedi.vim
34: ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/ftplugin/python/jedi.vim
35: /usr/share/nvim/runtime/ftplugin/python.vim
36: ~/.local/share/nvim/site/pack/mwchase/start/jedi-vim/after/ftplugin/python/jedi.vim
37: /usr/share/nvim/runtime/indent/python.vim
38: /usr/share/nvim/runtime/autoload/provider/clipboard.vim
```