front: Move some app-wide initialization stuff to SplashActivity.

SplashActivity is the first activity launched, so do all one-time-only/
constant data initializations there.

Basically trying to thin down MenuActivity as much as possible so that
it's easier to implement the new front screen for version 3.
front: Move language selection to action bar.

Get it out of the way for now.
front: Move language popup implementation to UserPrefs.java.

More compartmentalization of functionality.  The sharedprefs key is no
longer in any preferences.xml file. So we define the key in one place
only, as a private constant in UserPrefs, and shield the outside world
from the implementation.

Moving it here is also more parallel with the enforceLocale() method.
front: Completely encapsulate locale stuff inside UserPrefs.java.
res: Updated translations.
res: Fix string reference key in manifest.
res: Use consistent naming pattern for activity titles/preference keys.
res: Fix string key names in all translations.
res: Change a few key names.
res: Updated translations.
res: Remove unused strings.
front: Little fix to the language popup.

After install/reset, the popup would not have any language selected.
Could be a little confusing in some cases.

Also since locale is no longer tied to a preferenceActivity, we need to
define its default value elsewhere.
front: Refactor constant string.
front: Completely replace MenuActivity with GalleryActivity.java

Just a simple stub at this point.  Tap the button to select the ROM
file.  Should provide a good bare-bones starting point for implementing
the version 3 front screen.
res: Rename some resources for consistency.
front: Allow folder navigation in simple game selector.