Heat topology display improvement

The current heat topology display is poor because a lot of resources don't have any icons and are displayed as unknown resources.
Tasks to be performed are :
* Modify the openstack_dashboard/dashboards/project/stacks/mappings.py file to add the identification of the other resource types.
* Create icons for the others resources types, keeping the actual style and put them in the openstack_dashboard/static/dashboard/img/ folder.