Now possible to return to ScanActivity from NamePuzzleActivity or
PuzzleListActivity.

TODO: Cancel save and process tasks
TODO: Change color of grid cells in NamePuzzleActivity.
Now able to edit crossword grid in NamePuzzleActivity.
Limitations: Realized there is no way to make sure number of clues is
correct based on number of entries, unless OCR is guaranteed to work. No
way to automatically fill in right answer.

TODO: Add instructions at bottom of page for this.
TODO: Progress dialogs while scanning.
TODO: Ensure camera can resume after onStop.