Break Identity API into v2 and v3 pages

Add authenticate call to first page of api ref
Fix titles to match correct API versions
Added forward slash to beginning of all API calls
Added neutron to occurrences of OpenStack Networking
Other clean up

Change-Id: Ifcb51efa5996d083d9e6099c9b72b8faf39707b2
author: diane fleming
Merge "Break Identity API into v2 and v3 pages"