Migrate from DXF assets to IFC Project Library files

[brunopostle]

Currently the add-on reads DXF files for 3D assets such as windows, doors and columns, and 2D assets for extrusion profiles and assembles a Project Library for each style on the fly every time.

These project libraries could be written to disk permanently as IFC files and the DXF files discarded, this would allow the following:

• The ezdxf dependency could be dropped
• Users could create and edit IFC assets and other aspects of styles such as Wall Type and Material directly in blenderbim
• Openings could be any shape, currently arched openings need to be faked by including the arch in the Window Type
• Assets like windows currently have the same material applied, IFC assets will be able to have mixtures of glass, wood etc..

Issues that need resolving:

• [ ] A Project Library doesn't seem to have a standard way of associating Opening geometry with Door Type and Window Type elements. A Window can have OverallWidth and OverallHeight attributes, but a Window Type can't?!!
• [ ] Homemaker uses profiles for extrusions that follow a directrix, whereas blenderbim seems to only support depth extrusions in a Project Library. We also need Profile Set editing with multiple Material selection
• [ ] Currently each asset is a single DXF file, and only assets that are in use are loaded into the project, it doesn't seem right to import all assets into a project, but then it would be useful for a user to be able to browse alternative unused assets from the Project Library