Implement game generation timeout

[SteffenBauer]

As reported by TZornG in #17 , Puzzles with custom game parameters might not be possible for certain parameter values; causing the app to hang in an infinite loop. The app must then be terminated manually via the task manager, which is quite bad.

To be checked how to introduce a timeout; either directly in the generation loop of every game; or high-level by moving game generation to a separate thread. Quick-fix is to introduce more parameter limitation checks in affected puzzles.

[Skeeve]

Is there really a loop? Can't it just check on each iteration the time passed and bail out if it was too long?

[SteffenBauer]

(edit) Introducing a check inside game generation might be possible, but would take modifying every single game. Furthermore, for certain game parameters even a single generator loop might be too long.

I'm thinking of displaying a button during game generation where pressing it will cancel the game generator. Putting game generation into a thread might be the better solution here, but this is technically more challenging.