Attempt to cleanup addons on server leave (onDisable())

We need to create an AddonJanitor object that will remove all blocks/items/languages/screens/keybinds/etc (anything that an addon could register) whenever a player leaves a server.

We also need to fire onDisable and remove addons from the manager.

This is only for the client. Addons on the server should never be able to be removed during runtime.
