Plugin architecture

Small writeup of what i want:

core:
- XMPP (optional with "provides", so plugins can depend on it)
- Settings per plugin
- Enable/disable plugin
- External plugin?

plugins:
- Provides/depends (also core flags) - using Haxe metadata
- Interfaces for Main.hx and Settings.hx

settings:
- Generic API, with checkbox, select, radio, input.
