Added vibration when the game ends and for long presses
Fixed GameActivity to setup the minefield correctly

- Caused by not setting the minefield variable at the same time as
  calling MinefieldView.setMinefield
Added padding to MinefieldView

- This allows the user to see the edge of the minefield much better
Fixed bug where OnTapListener does not take padding into account
Various small improvements

- Changed background colour to black
- Added game over and game won toasts (popup messages)
- Moved vibrator constants (MinefieldView.java) to the top of the file
- Adjusted min and max zoom constants