More Updates

Fixed a problem with undoing a move (the pencil marks in the cell were not being restored properly) and a back-button navigation issue occurring after a user completed a puzzle and went to the History screen (it would go back to the still-editable puzzle); we also have the menu functionality done for undo, hint, validate, reset, and solve.  Selecting solve will replace all number keys at the bottom with an "OK" button that will bring them to the History screen and not record their score.  Score functionality is still waiting on implementing the timer.  I looked at some of that and may use a chronometer (an Android object) or a Handler of some sort to get the timer at the top to continue updating.  I'm also looking into the pause and resume functions - I think what I might do is make the pause return the user to the menu screen and they have to hit resume to keep working on the puzzle.  It should also do that when the user doesn't return to the puzzle before the app is closed by the system (can probably be done in an onStop or onDestroy method, I have to do more reading on the activity lifecycle).  I also need to figure out how I'm going to store it.  I was originally going to use an xml file or some sort of saved file, but I think there may be a more efficient way that doesn't require creating an external file.  More to research, anyway.