Basically if current mesh curve is non consequtive we handle it in similar way to b03c4da7b - convert it to curves using Blender and then save them to ifc.
The advantage is that it creates less curves in ifc because mesh method wasn't able to detect separate curves correctly if vertex order was messed up (usually it is) and it would create separate curve for each curve segment.
I've also replaced figuring vertex duplicates with `bmesh.ops.remove_doubles` manually with `bmesh.ops.remove_doubles` and it's now much faster. In some cases because of the manual calculations it was taking too long - in #3233 Ryan mentiones that it freezes blender, it wasn't really freezing Blender but to finish calculations it would take 10 minutes.
Now we do not rely on small offset to keep using inner curves to create linings, if some part of the lining is not present (which happens on mullions and transoms) we'll create U or L shape extrusion instead of rectangle with inner curve.
Long story short - this should keep ifc for windows valid.
From this - https://i.imgur.com/hQuCcR3.png
To this - https://i.imgur.com/qZ2Lyfo.png
It's a bit hacky since we still use really small offsets to keep "The outer curve shall enclose all inner curves." rule for IfcArbitraryProfileDefWithVoids valid.
Now blender curves segments saved in IfcIndexedPolyCurves instead of creating individual polygons.
Also changed ShapeBuilder.polyline - now it will try to store points in IfcLineIndex where it's possible (previously it was storing just 2).
Added support for sliding doors in IFC Door Modifier.
The main differences are 2d representation (https://i.imgur.com/VyEH569.png) and the door panel being placed before the lining, not after
Also:
- refactored window modifier code - part of it is now reused building a door and can be used by other module in the future
- fixed bug with window lining intersecting frame when lining_depth < panel_depth
- simplified the way lining is built in ifc - previously it was using 4-6 extrusions, now it's 1-2 which is also better for 2D drawings
* Bug when switching representations when active object not selected.
* Bug when switching to a non MODEL_VIEW body representation would load the MODEL_VIEW one instead all the time.
* Add support for plan body representations.
Dion Moult
