do not include auto-added packages like platform and arch in REZ_RAW_REQUEST
Simplify, document, and organize rez-env, particuarly the autowrappers/subshell feature, so that it is easier to add new shell types.  Move obsolete shell scripts into to_delete folder, so that we can keep them for reference while testing.
Factor out a common resolve() function for subshells and non-subshells.
Add support for package.py files written in python.
Don't add duplicate platform/arch packages.
pretty up utils a bit