Grid can now be set to read only so that users clicking on the view does
nothing.  This is handy in the NamePuzzleActivity.
Clues are now incorporated as part of the Grid class.  They are an
across map and a down map of clue numbers to Strings.  The
CompletePuzzleActivity pulls clues from these maps.
Clues are now serializable.  The grids can also be different sizes.  A
random grid is created when the camera is used now.  Next, need to
implement saving grid so it is playable.