Add port of scg04ea mission

This is a pretty straight-forward port of scg04ea.  I tried to keep it pretty close to the original, but made it a little harder in places by adding some reinforcements that were disabled in the original and making some units less passive on normal skill.

It's still quite easy, though. You can run through it in less than a minute if you're fast, and three minutes is well over par, I'd say.

There are few minor issues with this map:
* AFAICS a crate always assumes it has a CrateAction attached. So I chose the HealUnits crate to not make the crate do anything overly obvious.
* I work around the current lack of a cell trigger with Map.FindUnitsInCircle. Performance-wise not optimal, obviously, but on such a small map not really noticeable, either.
* The mission's title is too long for the map browser.

Needs #4854 to work.