Important Fluff

These are the additions in this update:

• Flipping a piece is now animated instead of instantaneous. I hope this will help players understand what "flipping" is doing and maybe it looks a bit nicer. 
• Reduced height of preview-field in change controls menu. With previews parameters it was possible to game over in the menu...
• The flip-failed-sound is played only once when a flip fails. Due to a bug that sound was spawned once every frame before.
• Quick guide menus, that show the basic controls without a lengthy tutorial. Impatient players, who hate tutorials, can now have a look at the basic controls and try to figure out how the game works on their own. The full tutorial is still available, for players who don't want to guess how the game works. Also, the quick guide is shown at the beginning of the game, if someone starts the game for the first time.
• The field previews in the menus spawn only  flippable pieces (pieces that change their form if flipped). Makes more sense for change control and quick guide menus.
• After game over a game over menu is shown. This menu shows some basic statistics (score, lines and so on). 
• Improved stability of background animation in menu, since the simulation became unstable sometimes. 
• The preview field in the menus is know randomly chosen to be a Dodetris or Icotris scene (before it was always a Dodetris scene).