lots of refactoring

 * plugins are structured as in mineflayer
   - lib/plugin.js is deleted
   - download, delete, lastfm, upload, dynamicmode disabled until they
     can be updated to work directly with PlayerServer
 * GrooveBasin class represents the main server
 * Killer is cleaned up
 * Library does not respond to bus; instead is constructed with
   musicLibPath
 * MpdConf is cleaned up
 * MpdParser is deleted in favor of mpd.js module
 * lib/player.js is deleted. wtf was that doing there?
 * server-side PlayerClient is deleted
 * PlayerServer is cleaned up a bit. ability to directly proxy mpd
   requests is deleted.