DocumentsFragment now extends ListFragment.  Created Loader, Adapter,
and data source interface.
Removed CourseFragment.  It's better to pass in the course id as a
Fragment argument.
Moved DocumentsDataSource interface inside of DocumentsFragment.
Deprecated CascadeDataSource interface for now.  The way it is used will
be changed.  Added test data for Documents to FakeDataSource.
DocumentsFragment now displays some fake data in a simple_list_item1.
Added asynchronous loading of course data to MainActivity.  Modified
CourseNavAdapter to use Course objects from the data.models package.
Added Course.toString()
Added a loading message when the Douments list is empty.
Fixed setEmptyText force-close bug.
Added framework for async loading to AssignmentsFragment
Modified AssignmentsFragment to use a static instance generator for
setting the arguments bundle.
AssignmentsFragment is now created using its newInstace() method.
Added Comment to CourseLandingFragment.CourseFragmentAdapter
Moved tab controls into CourseLandingFragment
Modified CourseLandingFragment to become CourseActivity.
Removed CourseLandingFragment.
Added the nav drawer to CourseActivity.
Nav Drawer closes on clicking an item.