fixed 'More releases and languages...' dropdown menu

Also fixed URL of /themes/openstack/css/dropdown.css. The file is
only available on openstack.org and not on docs.openstack.org.

Also cleaned up the syntax of common/css/docblitz.css.

Change-Id: I0b6ab58d7887c1df3b5e52937c6f6902fa995f97
Closes-Bug: #1318480
Merge "fixed 'More releases and languages...' dropdown menu"