Use Right Click for Minesweeper flag placements

https://github.com/shoes/shoes4/issues/521

There was a small issue in this sample where the right click and middle click buttons were swapped. This pull request modifies the game so that right click reveals a flag and middle click clears a section of squares. Also, since   I am using the new mouse constants in this game, I decided to switch them in both minesweeper examples.