Refactor settings top level activities to use fragments.

Added a base class SettingsPreferenceFragment from which the settings activities should
be derived so that they can behave like fragments. It contains some commonly called
utility methods and dialog conversion to DialogFragment.

Some of the top-level activities can be launched directly without the left pane.
Settings.java acts as a proxy activity that contains just that settings fragment without
the left pane.

There are still a lot of second and third level activities that need to be fragmentized.
This is just the first pass to test the 2-pane layout.