Updated OCC logo.
Replaced some external links to https.
Added references to VS2019 support.
Added glTF, OBJ, IFC, JT into listing within appropriate sections.
Replaced dead URLs.
Fixed misleading information.
Description of building OCCT with WOK and automake scripts is removed from documentation.
Use of genproj utility is described in pages on building with MSVC, Code::Blocks, and XCode projects.
New script genconf allows starting configuration GUI explicitly; dialog is slightly revised.
Script genproj.sh is renamed to genproj; permissions for scripts are corrected for Linux.
Script env.bat does not set anymore environment required for Products.
