Base, enemies and more to come

There's a new object in the middle of the area, which is the base. You'll have to protect the base and stop enemies from reaching it.

Oh yeah, we have our first enemy. They are pretty dump for the time being and just try to find a path to the base. We'll expand on this tomorrow.

Fences and workers can no longer be picked up. Yes, you'll have to drop resource blocks in the work area :)

The beam looks slightly better, fixed some related Z-order issues.