There isn't really any need for these two types to interact. The lua
plugin manager effectively fully owned its properties, it just delegated
all reads and writes to the settings object.
Instead, break the plugin settings out into the plugin manager and
preserve the manager in the Game. This will make it possible to expose
plugin options in the NGW without breaking the game on cancel.
Trying to fix the singleton-ness in the plugin manager because it
prevents injecting settings until the game is fully committed (new game
wizard completed). Added the docs describing what I think I've been able
to discover.
* Move the UI code out of the plugin logic.
* Add types where needed.
* Move into game package.
* Improve error handling.
* Simplify settings behavior.
* Don't load disabled plugins.
* Remove knowledge of non-base plugins from game generation.
Fixes https://github.com/Khopa/dcs_liberation/issues/311
