various improvements (based on user feedback) and minor bug fixes

• V1.7.2
  • added the --wfe_host and --wfe_host flags to "ck start web".
  • improved API when starting CK server and a browser at the same time ...
  • added info about Docker support in CK
  • simplified adding remote repo using --hostname --port --hostext
  • added possibility to describe repository for Artifact Evaluation
    using flag --describe (see http://cTuning.org/ae), i.e.
    ck add repo:my-artifact-pack --describe
  • return 16 when adding new entry (including repository) and it already exists
  • added often used 'load_yaml_file' and 'save_yaml_to_file' functions to kernel
  • changed yaml.dump to yaml.safe_dump
  • added --install option to "ck pull all (--kernel)" to install CK kernel as python module