Change handling of last level.

The last level now throws a "win" event which can be picked up by the
frontend. The unreachable "buffer" level is removed.
Remove the performance-heavy scientist progress bars.
Pick up on the "win" event and show a dialog for it.
Various minor performance/stability fixes.

* Don't crash when no info about the next level is found;
* Don't pass the scientist progress anymore (not used);
* No more bankruptcy once the game is won.