regular extensions based on user feedback

• added support to automatically add simple packages from Git:

   ck add package:my-git-repo --git={URL} --tags=my-repo --env_ext=MY_GIT_REPO

• added module:mlperf.result to abstract official MLPerf results
• added key "skip_global_deps" to program meta to skip global dependencies
  for a given command line (for example, only to install python deps
  for a given program)
• improved handling of a situation when CK environment has changed
  and make it possible to continue running a workflow at user risk
  (useful for debugging)