Set notification action to always appear
Add help action to the action bar
Hide activity-specific actions on nav drawer open

The Android design guidelines suggest that activity-specific actions
should be hidden from the action bar when the navigation drawer is
opened. Otherwise, the user may expect the actions to apply to the
drawer itself.

To achieve this, extract the application-wide actions into a separate
menu resource which is inflated by `DrawerActivity`. Subclass activities
will inflate their specific actions from their own menu resources. When
the navigation drawer is opened/closed, the activity will automatically
hide/show those actions added by the subclass.