Merge pull request #329 from lioncash/master

[Android] Decouple a large amount of preference handling functionality from the MainMenuActivity in the Android front-end. Along with numerous simplifications/optimizations.
(Android) Some preliminary changes for new libretro core naming convention - still not
working here
(Android) Changes for filename naming convention changes
[Android] Made DirectoryActivity extend a ListActivity, since that's basically what its purpose is - to act as a list view.