Plugins

This branch converts teeveed to a modular, plugin-based architecture. the skeleton of the app is responsible for only three things

1. Startup, options parsing, and loading user configuration (teevee/daemon)
2. library indexing and management (teevee)
3. running plugins on Wit intents (teevee/plugin)

the following features are now plugins:
- the on-tv HUD is now `heads_up_display.rb`
- finding episodes/movies for VLC playback is `play_videos_with_vlc.rb`
- pry-based debugging is now `remote_debugger.rb`
- the webapp is now `web_ui.rb`