Create plugin management UI

Using `SimplePluginManager` as the back-end:

UI should provide:

- Tab for local plugins
- Local plugins placed in `%RECAF%/plugins/`
- Allow toggle on/off plugins _(should be persistent)_
- Allow easily loading new plugins
- Allow easily updating plugin if a new version is found _(Can support official plugins, see below)_
- Tab for remote plugins
- We can use the github API _(rate limit to only check once per day)_ to scan for all releases under:
- Or figure out some other scheme, ideally a freely hosted one that allows easy discovery and is easily updated as a maintainer
- Show most recent release's changelog _(Can refer to the Recaf 2X updater on how to render MD/HTML from release, or make something better)_
- Allow one-click download / immediate install