Fixed problem with pure referencing.
To export reference label to step we convert it to the assembly with one part.
All attributes attached to the label should be moved to the new part.
For working with it new map contains only pure reference labels, that converted to the part
was implemented to the STEPCAFControl_Writer.
Updated code style of the STEPCAFControl_Writer
Improved ability to export labels from different documents
Removed OCCT_Debug macros to print in Trace gravity
