Add "bad flag" logic. Move "red mine" logic to Board class

The game now shows you where you have made a mistake during
the flagging. This changes the way defeat reveal works so that
it now shows you the correctly flagged mines and the not so
correctly flagged squares.

Also the "red mine" logic which previously existed only in the
GUI is now moved to the Board class. "red mine" is the mine
that triggered the defeat. Now it is possible to have such
a feature in the CLI as well, although this was not added to
avoid the explosion of different symbols.