Play with persistence
Improve presentation context for modal views: use the navigation controller or the topmost modal view.
Debugging support and cleanup
Add a debug switch (deactivated) to watch the view controller callbacks.
Open issue (c) fixed in svn 3555. (a) and (b) are still open.
Persistence: fix single card from drill. Note: this is one of the open issues of #435.
Prepare a method to find a context for presentation.