[feature] Remove construction sites when out of spawns

[tedivm]

If someone clears a room out a construction site for the first structures they hit will be placed, but once they clear out the spawns nothing will be able to build it. Clearing out other sites will make the spawn build quicker and help the room recover.

[TheRealMaxion]

Alternatively the placement of a spawn site could bypass the 1 site at a time rule