Theming support.

Light, dark & black theme available. Not all are done yet.
The switcher in settings smoothly transitions the different themes.
ThemeHelper added with helper function ThemeHelper.setTheme(Activity) to
be used in Activity.onCreate to set the theme.
LoaderPool: check instance of Loader, not just equals

While only checking equals seems like a right choice,
the list position is not shared anymore this way.
Finished dark theme and added black theme.
Merge branch 'master' of https://github.com/Floens/Clover