Lock reverse mode and bring unlock animation back

[supertuxkart-sourceforge-migration]

Author: hikerstk

Reverse mode should be locked, and instead one more track should be unlocked (since atm there are only three tracks unlocked from the very beginning).

Can easily be postponed till 0.8.1

Migrated-From: https://sourceforge.net/apps/trac/supertuxkart/ticket/773

[supertuxkart-sourceforge-migration]

Author: hikerstk I'll unlock all tracks so that the first GP can be played without story mode.

Also try to get the 'unlock' notification back.

[supertuxkart-sourceforge-migration]

Author: hikerstk In r12090 all tracks of the first GP were unlocked initially, though the first GP is still locked in non-story mode.

Assigning this to auria to fix the unlock animation (and perhaps lock the reverse game mode - not sure if that might break the string freeze).

[supertuxkart-sourceforge-migration]

Author: auria The unlock animation is now complete. What's left is locking reverse, but that can wait

[supertuxkart-sourceforge-migration]

Author: auria Not required for 0.8.1, wasn't there in 0.8 either