+ include missing header file
Have cmake set doxygen to use dot if it's available.

Also a minor typos
Forgot to add this to the last commit...
+ Mesh trim loses some triangles
+ fixes #0001499: Mesh trim loses some triangles
Arch: General improvements

* Removed roundings in exported objects
* Added toggleIfcBrepFlag command to force export as BREP
* Prepared Arch objects for Materials and custom IFC attributes
* Supported latest developement version of IfcOpenShell
* Cleanup of IFC exporter
* Export of Arch Sites as IfcSite
* Export of Groups as IfcGroup