Polish GDI01 and 02.

This fixes the landing craft in both missions, and includes additional tweaks to GDI01:
* Removes unbuildable concrete wall from production palette.
* Fixes chat sounds and reinforcement notification overlapping FMV.
* Cuts down the excessive starting forces to encourage base building.
Yes, please do. It's too low-level for my taste, and if we introduce it now we need to keep it and support it. If it turns out that we need it after all we can always add it back.