Titlescreen fix for issue #13 - part 1

Title screen added with 3 menu buttons (start, instructions and exit).
Instructions has no functionality yet.
The title screen is missing some design too.
GameOverScreen added to issue #13

Now there's a game over screen with buttons to main menu (title screen),
restart and exit.
Instructions part 1

Started adding instructions screen
Instructions finished

Instructions screen is now working. Still it needs some design.
Fixed #13 - Title screen and gameover screen

Title menu with 3 buttons (start, instructions and exit) now working).
When looking at instructions you can go back to title menu.
When all but one player in the game screen are destroyed, the gameover
screen will load and present the winner (and some random scores). This
screen has 3 buttons (restart, main menu and exit) all working.
Merge pull request #17 from Martichoras/Iss13

Iss13 into master