Fixed crash reported via Play.
Fixed crash on state restore.

This was due to the context being held getting nullified after the application has been killed.
The context was not actually needed to be stored.
This is also the correct fix for an issue reported through the Play store.
Themed DialogFragment titles.

Created a special subclass that relies on internal android layouts to apply the styling. For more info see the DarkTitleDialogFragment documentation.
The dialog title theming does not apply to dialogs in Settings.
Also changed some of the dialogs' icons.
Closes #5.