db: add watched column to episodes table
Place a "watched" checkbox next to each episode in list

Place a checkbox next to each episode in each item in
EpisodesListFragment. Use a ViewBinder to display it as either checked
or unchecked based on the value of the corresponding row's watched
column.
Use custom CursorAdapter subclass in EpisodesListFragments

Instead of SimpleCursorAdapter. This will allow access to the
individual widgets in the future.
Update episodes' watched column when checkbox is checked/unchecked
Add menu item to mark an entire season's episodes as watched