Windows: file operations don't always succeed as expected

### Problems

- shutil.rmtree or os.remove does not always ensure that files are fully removed after function returns
- remove may take multiple attempts to succeed
- mkdir(path, exist_ok=True) might have a race condition if it is called just after the folder is "removed"

### Related Issues
- https://github.com/07th-mod/python-patcher/issues/33#issuecomment-489390131 "07th Mod - Install failed due to error: [WinError 145] The directory is not empty"

### Description

I noticed that sometimes in `travis_build_script.py`, try_remove_tree() didn't always remove the file immediately (the file would exist for some time after the function was called. The function used to be defined like this:

```python
def try_remove_tree(path):
try:
if os.path.isdir(path):
shutil.rmtree(path)
else:
os.remove(path)
except FileNotFoundError:
pass
```

but I changed it to this

```python
def try_remove_tree(path):
try:
if os.path.isdir(path):
shutil.rmtree(path)
else:
os.remove(path)
except FileNotFoundError:
pass

# Make sure the folder is really removed
poll_cnt = 0
while os.path.exists(path):
print(f"Waiting for {path} to be removed ({poll_cnt})")
if poll_cnt < 5:
time.sleep(1)
else:
raise Exception(f"Folder {path} could not be removed!")

poll_cnt += 1
```

The `# Make sure the folder is really removed` did trigger on my machine (at least once), and after 1 second the file was "properly" removed.

If this behavior can happen on windows, we should also update the installer scripts, which use the same functions, to add this kind of functionality.

The installer scripts currently don't do multiple attempts when doing operations like extraction, deletion etc, so it may be worth checking for those sort of issues as well.

Veja travis_build_script.py para a função try_remove_tree e os scripts de instalação que realizam operações de arquivo. Entenda as condições de corrida específicas do Windows com shutil.rmtree e os.remove. Teste o mecanismo de polling e considere aplicá-lo a outras operações de arquivo na base de código.

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