Create plugin for OpenStack Client

The OpenStack client (http://docs.openstack.org/developer/python-openstackclient/) has a plugin framework which would allow addition of App Catalog search, fetch, add and update functionality. Adding this would enable easy CLI access to the catalog. First step should be implementing search of the catalog V1 endpoint, and fetching assets from the catalog (similar to what the app-catalog-ui horizon plugin does).

When the API can accept authenticated additions to the catalog via API, we can extend the web site, horizon plugin, and OpenStack client to add content that way rather than via editing the assets.yaml. At this point we will require additional entries to be made via API rather than via updating the assets.yaml file.