Migrate from ActionBarSherlock to AppCompat

A couple of main reasons to do this:
* Android L will have some UI components that we will want to use in AppCompat (RecyclerView in particular), and ABS doesn't play nicely with it.
* The AppCompat 2.3 menus don't include icons, making menus nicer looking and their assets significantly easier to manage.
* ABS is at end of life
* Simplifies our multiple PasswordRequiredSherlockActivities, all ActionBarActivity objects support the compat fragment manager

This also uses the support-v4-preferencefragment library to also include support PreferenceFragment objects, since AppCompat fails to include it. The biggest file diff is just creating an ApplicationPreferencesFragment and using PreferenceFragent instead of the deprecated PreferenceActivity.