Added some files for header menu
Header menu icon added
Changed menu icon to restart icon
Added game over logic if square with mine is hit

If the player clicks on a square with a mine the game will enter
a game over state.
WIP: Added restart feature

Added restart feature but the board is not updated properly when the
restart command is given.
Fixed the update of the model when restarting

It's now possible to restart a game that is game over. This will
redraw the board with new squares.
Merge branch 'feature/game-logic-and-restart' into development