Remove old Core Data model versions.

Core Data's finally, officially just a cache, and I don't care if it gets
migrated anymore.
Stop using mogenerator.

I'll just update the classes myself.
Remove old Core Data migration that extracted favorites into user defaults.

I don't care about anyone who hasn't yet updated to the point where this is
fixed.
Clean up and make explicit use of managed object context.

- Remove migration code from AwfulDataStack.
- Explicitly pass managed object context (or an object therefrom) to view
  controllers, managed objects, and other objects.
- Fix AwfulForumListController's state preservation.
- Directly save the relevant managed object context.
- Rename managed object model and explicitly refer to it.
- Move Core Data models and related code to "Data" folder.
- Remove data stack will/did reset notifications. If a replacement is needed,
  use NSPersistentStoreCoordinatorStoresWillChangeNotification and check if any
  stores will remain.
Delete unused "start view controller".
Rearrange Data group in xcodeproj.
Forums list controller no longer is its own restoration class.

We want the app delegate to handle things, which only happens if there's no
restoration class set.
Reload the forums list after restoring state.

The table view's row data is invalid once the tree controller is restored.
Bookmarks controller doesn't need a restoration class.

App delegate can handle it.
Redo posts view controller API to take actual objects.
Bookmarks controller no longer inherits from thread list controller.

Never really made sense. They do share lots of code though, should factor that
out.
Push tab bar under status bar, keeping first tab visible.