draw surface normals on all windows and walls and roofs

[ChrisZenhub]

[ChrisZenhub]

as per discussion: "what if window centroid coincides with wall centroid"? -> hardcode threshold to check coinciding centroids, if yes, randomly move one arrow away, -> assign different drawing properties to windows and walls (e.g., dashed vs solid lines, etc.) -> ..?

[ChrisZenhub]

careful with the grasshopper example above; it turns it into a mesh and then we might have multiple centroids per surface. -> better directly work with original surface. (careful: untrimmed vs trimmed surfaces)

[philipschulz]

this does it