Add quota support to Openstack Tenants

Adds support for collecting and storing openstack quota details form various openstack services.

Backend updates:
* Adds `cloud_resource_quotas` table and models
    * with STI to support OpenStack specific quotas
* Updates Openstack inventory collection
    * fixes the way that openstack tenants were collected
    * collects quotas based on services and tenants
        - e.g., in Tenant "ABC", the "compute" service allows for 30 vCPUs

UI Updates:
* Tenant tab in Cloud subnav
* Cloud Tenants in Openstack provider relationships lists (listnav and textual summary)
* Security Groups, Instances, and Images relationships for Tenant summary page
* Quota on Tenant summary page

NB:  Rebased this PR to remove the references to the Tenant Auth support.  I've got that stashed away as a separate branch for now.  If it turns out we still need that concept, we can go back to it.  For more information, see @roliveri's comments on outdated diffs below.

@Fryguy, @roliveri, @dclarizio, @h-kataria please review
throwing this out there:
```
  <%= link_to_with_icon_or_none(@record.number_of(:security_groups) != 0,
                                 "Security Groups (#{@record.number_of(:security_groups)})",
                                 {:action=>'show', :id=>@record, :display=>'security_groups'},
                                 :title=>"Show all Security Groups") %>

def link_to_with_icon_or_none(display_link, name, link, attributes)
  if display_link
    link_to_with_icon(name, link, attributes)
  else
    image_tag("/images/icons/16/link_none.gif") + name + tag(:br)
  end
end
```