Remove unnecessary ldpi icons.

Android scales down hdpi icons 50% for ldpi devices. Also, they're not that common nowadays.
Redrawn, vector based graphics.

Also adds xxhdpi and xxxhdpi icons (requires API v16 and v18, respectively, hence no Gingerbread style icons there).
Bump version, target Android SDK v19.
Update copyright in modified files.
Move preferences.xml to a more "correct" location.