Shadow Threshold, April 18, 2014, Changed to 40%
User select square if same square tapped and released, April 24, 2014,
Use mDownCell variable to track
Fixing squares responds to touch too easily, April 24, 2014, Switch to
mDownCell (cannot use onClick for selecting cells)
User select black square causes crash, April 24, 2014, Change
onCellSelectedListener to return selection successful
Tapping during scanning causes crash, April 24, 2014, OnClickListener
does not register after photo taken