0029830: STEPCAFControl_Reader poor performance - quadratic dependence

0029830: STEPCAFControl_Reader poor performance - quadratic dependence

Various performance improvements in STEP read/write algorithms:
- Search for the  label of a shape or component shape is improved using map mechanism instead of brute force iteration.
- Invariant FindEntities() is moved out of the loop in the method getStyledItem in STEPCAFControl/STEPCAFControl_Writer.cxx.
- A pointer to the end of binders chain is added in Transfer_Binder class to speed up adding a binder to the chain.
- Small fixes are added  to eliminate excess copying of handles, calls of handle DownCasts and so on.

Stack overflow is removed during destruction of STEP model with long chains of Transfer_Binder.
It is possible to use the Draw commands ReadStep and WriteStep to read/write from the session without accessing the disk file (use '.' for the file name).

Performance test cases for STEP reading/writing have been added.