Small Menu Drawer Item refactor

While preparing to put in a new menu item I found it a little difficult tracking all of the places in `WPActionBarActivity` that tracked which menu items are available/highlighted and what to do when they were selected.

Since the `MenuDrawerItem` class already existed this expands its functionality and provides a way to configure visibility/selection state and its action all in one place.

The main gist is that `WPActionBarActivity` now as a private list of available `MenuDrawerItem`s. When updating the menu each item is asked if it should be displayed. Then in the `AdapterView.OnItemClickListener` picks the `MenuDrawerItem` off the `MenuAdapter` and fires its `onSelectItem`.