fixes #1319
allow Part.makeHelix to use 'vertical height' parm
correct lefthanded conical helixes in TopoShape::makeHelix
Add initial support for different libdir (jobermayr)
+ add '_' as prefix for PartDesign module to fix name clash
Arch: Big cleanup - fixes #1524

* Removed redundant code in Arch objects
* Supports wandererfan's Units code in Draft module
* Cleanup of the IFC exporter
* Better support of extruded profiles in IFC export