Aysnc prefs

Here are the async prefs on a separate branch. I removed my old work and rolled the new prefs. As far as brackets is concerned, the API is still synchronous. I created a requirejs plugin to load the preferences before anything else.

Basically the only thing that has really changed is the PreferenceManager. All other changes are either: 
 * Calling require with the plugin (minor change)
 * new files
 * reverting back to the way it was