[www] update dropdown menu for Liberty
[www] update dropdown menu for Liberty

Remove Icehouse, add Liberty as current release.

Change-Id: Ie1041000523747a23b217351bafb8ce2f5318507

AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals