Tracking issue for material and styles revamp

[Moult]

The way the material and styles currently works was because that was the best way I could work out how to do it to align with Blender's native "materials" tab.

I'm slowly working on building a proper IFC-oriented styles/material manager which can handle styles properly (e.g. style-material association, or representation item styling). This should really improve a lot of the user confusion around how styles works, and solve a number of bugs, such as:

• When using an external surface styles, it doesn't seem to pull in material settings from the external material.  #4053
• assign_representation_style can only style an IfcGeometricRepresentationItem #4038
• Original style of object is lost after duplicate and refresh #3893
• Be able to remove and apply external surface styles #3861
• bim.update_current_style does not work with certain materials #3848
• Style disappears after editing door #3593
• 'create an IfcMaterial' and 'create a IfcStyle' directly from the Geometry and Materials tab. #3543
• Relocate remaining material panels under the Geometry and Materials tab.  #3542
• Easy way to create a new ifc material at typical dropdowns #3452
• Automatically assign IfcMaterial and IfcMaterialConstituentSet #3395
• Switching shading mode to rendered doesn't switch to external styles for new viewport areas #3296
• bbim display color of elements colored by IfcSurfaceStyle #3199
• Keep vertices separated in Types #3120 (partially)