0031481: Data Exchange - provide parser of STEP EXPRESS schema for generation of...

0031481: Data Exchange - provide parser of STEP EXPRESS schema for generation of new STEP entities

Integration of ExpToCas tool ported to modern state of OCCT:
- new package Express and toolkit TKExpress for EXPRESS data structures and OCCT class generator
- executable ExpToCasExe including lax/yacc parsers, for parsing a Part 21 file and generating classes

Off-topic: genproj.tcl is improved to
- deal correctly with FILES files containing CRLF end-of-lines
- generate one project per executable unit (instead of one project per cxx file); note that this matches behaviour of CMake generator