Reorganize api-ref: v3 project-tags
Reorganize api-ref: v3 project-tags

Reorganize as per the documentation session at PTG:
https://etherpad.openstack.org/p/queens-ptg-keystone-doc-cleanup

Change-Id: Iad37863f30fd805608c0532d5a5d4207a373e5e8

openstack/keystone,openstack/keystone,openstack/keystone,mahak/keystone,mahak/keystone,mahak/keystone