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
Introduced new attribute XCAFDoc_VisMaterial storing visualization material definition.
XCAFPrs_Style has been exteneded Material() property.
XCAFPrs_AISObject::DispatchStyles() maps new XCAFPrs_Style::Material() property onto graphics aspects.
RWGltf_GltfJsonParser and RWObj_CafReader now put Material definition into XCAF document instead of a color label.
RWGltf_MaterialMetallicRoughness - added missing properties AlphaMode, AlphaCutOff and IsDoubleSided;
fixed default values in constructor for Metallic and Roughness.
Added commands XGetAllVisMaterials, XGetVisMaterial, XAddVisMaterial,
XRemoveVisMaterial, XSetVisMaterial, XUnsetVisMaterial for working with
new visualization materials table in the document.
