PreferencesModel declared at higher-level

Ran into an issue of the Preferences not being session persistent
because I had been declaring in wrong location
Added Preferences Manager

(incomplete!) Loads/Saves PreferencesModel's to disk
Added missing JavaDoc to PreferencesController::getSfxVol()
Preferences Manager Loads Preferences and Populated to Preference Window

- Save Work
- Automatically Loads Preferences when window is opened

TODO: Clean up the code and figure out when we should load the
preferences (before opening Pref window is not the right time, they need
to be loaded early for the game to use)
Merge pull request #203 from BU-CS673/Ethan-Staging

Ethan staging