Massive code cleanup.

edu.dcc.crosswordscan.CompletePuzzleActivity:
Reset cursor to first cell on puzzle reset.

edu.dcc.crosswordscan.ScanActivity:
Define photo button behavior via XML reference.
Use future to obtain result from SavePhotoTask on button press.
Currently returning path of created photo.
TODO: Figure out how to pass photo to next activity.

edu.dcc.game.CrosswordGame:
Changed usage of acrossMode and reset it when puzzle reset called.

edu.dcc.game.CrosswordGridView:
Based on user feedback, move cursor only to empty cells when navigating
puzzle.
Change implemented in nextClue and moveCellSelection.
On reset, moves selected cell to first white cell.
TODO: Move to crosswordscan package.

edu.dcc.game.Entry:
Changed name of size field to length.

edu.dcc.game.Puzzle:
New class consolidates Grid and clues into single class.

activity_scan layout:
Added camera icon and made button transparent over camera view.