Feat/remove bottom

[ipadjen]

Added remove_bottom option that removes faces at the overlap of buildings and terrain. How it looks from the bottom:

Some key takeaways:

• It works good when the terrain resolution is similar to buliding edge length (edge_max_length vs terrain horizontal resolution)
• Imported building should probably be remeshed before being imported.
• There is no 100% guarantee that there won't be (small) openings at the intersection of buildings and terrain, but it should work fine if the point 1 is satisfied.

todo after merge:

• Add info to config in wiki