Fix for broken pop jobs...

Pop assembly speed also reduced now, so machine empires won't be OP.

Increased required pops for planning/building new habitats.
Reduced pop growth on habitats by 50%.

Fixed ai - they weren't able to build habitats at all.

Major Update:

Added Districts:
-Asteroid Mining Module
-Turbine Module
-Promenade Module
-Aeroponics Module
-Crystal Gallery Module
-Synaptic Module
-Network Module
-Biotrophy Module
-Leisure Module
-Maintenance Module
-Artisans Module

Changed Districts:
-Culture Module
-Foundry Module (formerly Heavy Industry Module)

Added Civic: Xenohabitation

Changed Modifier: Hostile-Environment Habitat

Added Modifier: Orbital Habitat

Added Colonization Limits:
-Planetary Habitats require no planetary habitats that are uncolonized or have less than 5 pops.
-Orbital Habitats require no orbital habitats that are uncolonized or have less than 10 pops.

Blockers Changed: Planetary Habitats should start with fewer blockers now, but they cost Alloys to remove.

Orbital/Asteroid Habitat Expansions Changed: They're a little more expensive now.

Misc. Fixes
-AI should spam districts a lot less when they don't have pops to work the jobs. If you see a district being spammed without employable pops, let me know so I can fix it!

Changed ai pop requirement from 15 to 10, so they stall out less often. (hopefully never.)

add stpg_planetary_habitat flag to planets

Changed name of orbital/asteroid/gas giant housing modules to "Low-G Housing Module"

Significantly increased required pops on other habitat worlds before AI can plan/build new ones. Should help reduce late-game lag.

Mastery of Nature can now be used on barren, molten, toxic, and frozen worlds. It costs some alloys and a bit less energy.

I plan to eventually rework this so that the habitat version is more different from the standard version. But it's a starting point.