Cleanup Lua plugin implementation.

* 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

resources/plugins/base/plugin.json

@@ -1,5 +1,4 @@
 {
-    "mnemonic": "base",
     "skipUI": true,
     "nameInUI": "",
     "defaultValue": true,