Added roofs to greenhouses

[PatrikLundell]

Summary

None

Purpose of change

Add roofs to greenhouses.

Describe the solution

Add nested roof chunk to greenhouses.
Adjusted chicken coop to explicitly not have roofs, as there's nothing to support any roof.

Describe alternatives you've considered

• Deal with churches using natural stone floors.
• Rework chicken coop to have roof, e.g. by providing corner supports.
• Remove pigeons from coop since they'll just fly away (and still would if roofs were added, since they can fly over the fences).

Testing

Changed the odds for greenhouses to show up in buildings using these chunks and verified they did show up with roofs. Made sure the three variants did appear correctly, but did only verify at least one of them appeared on each of the buildings using them (and showed up correctly).
Checked that the chicken coop looked OK in one using location.
The two first greenhouse variants on the cathedral (with it natural stone floor roof):


The third variant (note that the garden to the left isn't supposed to have a roof):


And the chicken coop (no image of the non existent roof, since it doesn't exist):

Additional context