Removes unused imports as reported by LGTM.
There are exceptions: `import Arch_rc` is shown as an alert, but has side effects. It's not clear what the best thing to do in those cases is, so I've left them for now.
* The import code will manually set 2x3 attributes
* The import code will rely on "smart" attributes for ifc 4
* ArchSite and ArchBuildingPart now support IFC
* IfcSite lat/lon is left alone until I better understand how coords work
* Properly handle offset2D and arch objects in Draft Stretch
* Allow the WP of Arch BuildingParts to stay weak
* Fixed Draft Edit making Wires not plane anymore
* Dont change the WP if already perpendicular to current view
* Fixed DXF import of Polyfaces
