[x] Add effect to end of game (when you win)

[mtedeschi]

1. The fish reach the end of the game. The game stops scrolling (ideally, we ease down instead of a hard stop) before the PNGs end so it ends naturally.
2. The fish continue swimming from their original position all the way off-screen to the right (ala Sonic the Hedgehog).
3. The congratulations screen comes up during this transition or immediately after it.

[tespenshade]

added in, sonic-tastic!