Remember traps&events

Makes known traps and event generated terrain effects remembered on the map and minimap (with distinct colors for each).

Fixes some bugs that were causing the nice tiler to overwrite modified grids for some events.

Makes overlapping event terrain effects behave nicely.

Adds "Lua inspect [Trap]" to the map menu in debug mode.

Note: May need new particle effects to make remembered area effects out of LOS look better.