Fixes an exploitable bug that allows for certain ID challenges to be completed...

Fixes an exploitable bug that allows for certain ID challenges to be completed prematurely by zoning out to a major event level.
Instead of resolving on any level change, challenges are automatically resolved on death or when entering a new ID level.  (The quest on_exit_check function is only run after the level change is complete to allow the destination to be determined.)
This allows the exterminate, pacification, Rush-Hour etc challenges to continue when entering a hidden vault, for example.
The ZONE_AURA_CHALLENGE persists across levels if applicable and some quest text is clarified.
Death always results in challenge failure (unless already successfully completed).

Specific changes:

Pacifist: Death or zoning to a special event level will not trigger immediate success

Exterminator: Zoning to a special event level will not trigger automatic failure

Rush Hour: 20 more turns to complete, continues to count down (with warnings) in a special event level (must exit to the next ID level)

Fixes a bug in GameState:startEvents that was not checking for special function for major events with events_by_level set.