Colony size limits

**What do you want to see?**
SE2 had a limit on colony size on a planet depending on what kind of colony module you used to colonize it. This idea came up again when implementing #159, specifically the similarities between ships containing components, colonies containing facilities, and planets containing colonies. What does colony space mean on a planet? Just hardcode it at 1 for now and make all colonies take up 1 space, but could this be expanded on?

**How would it help players?**
Features for modders to play with

**Alternatives**
see #319

**Screenshots and mockups**
N/A

**Things to consider**
How would this limit be enforced?D