Revert "[Android] Move the main activity to use Fragments."

This is pretty pointless at the moment actually.

This reverts commit bfdc1e0e601a85db973adc49215e5c77719e2d7e.

- Keeps some modifications to the MainMenuActivity. Most notably the title string retains itself upon orientation changes.
- Also fix some bugs in the PreferenceListFragment. Most notably, the handler message not being removed.