Provide a resource summary

An often sought after use case is to find a summary of all the things in the cloud.

This would either expand plugin-info to include resource summary, provide a new API, or include summary in facets.

eg. By default include it for the current project:

{
    "plugins": [
        {
             "name": "OS::Glance::Image",
             "type": "OS::Glance::Image",
             "index": "searchlight",
             "count": "123",
             "count_all_projects": "345"
        }
    ]
}