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.