This commits prepares edx-platform's experimental Dockerfile
for optional use in devstack. Presently, the image built by this
Dockerfile isn't used anywhere.
Notable changes:
* Drop the openedx/edx-platform image name in favor of
openedx/lms and openedx/cms.
* Drop the newrelic stages and tags.
* Create openedx/lms-dev and openedx/cms-dev image
variants which use Django devserver, install dev
requirements, and specify devstack Django settings.
* Add config files at (lms,cms)/envs/devstack-experimental.yml,
extracted from the existing edxapp docker image.
* Adds three new scripts, each of which replaces an Ansible
or Paver-supported function with a pure bash + Django
management command implementation.
