Document another pitfall in the Lua API
Make crates not suck

* allow for crates without any associated CrateActions
* allow for crates to not auto-remove
Fix crates in gdi04a/b
Fix chat sounds overlapping with playing FMV in missions
Enable fog in TD missions
Prevent viceroids from appearing in missions
Merge pull request #6837 from obrakmann/mission-polish

Another mission polish PR