Changes

0033551: Visualization - Add new transform persistence mode to force orthographic projection on object.

The new transform persistence mode, with flag `Graphic3d_TMF_OrthoPers`, can be combined (bitwise OR operation) with the other persistence modes (2D, Trihedron or Zoom/Rotate Persistence) to make objects be rendered with orthographic projection when it is on a view with perspective projection.

If the view already uses orthographic projection, there will be no difference.

This feature was implemented to fix ViewCube being distorted when view with perspective projection changes size.

0032980: Data Exchange - STEP import produce a crash

Check on null for loop added

0025188: Data Exchange, Step Export - Losing shapes after import

Check on null for description added to WriteStep methods
(for product, product_definition and product_definition_formation)

0033569: Data Exchange, STEP - Crash when reading multi-body file

Datum reading changed in ReadDatums() method:
using DatumSystemAP242 (DatumSystem or DatumReference) array
instead of DatumSystem array (DatumReference)

0033261: Data Exchange, Step Import - Empty shape after reading process

Added a transfer for ShapeRepresentationRelationship in Transfer of MappedItem method,
in order to support link of components according to ISO 10303-203-2003.