Cleaned up navigation after v2.1.
Made navigation through menus and docs consistent as to when to remain in an extension or to force to basic schema.org. Included making schemas.html into a template.
Also maintains the http/https state through a user session.
Corrected thread based caching of global variables errors that were introduced with extensions - reset temporary fix of threadsafe=false in app.yaml.
Introduced a /_siteDebug page to monitor cache usage and settings etc.
(#429) - Completing the initial extensions model
(#732) - Docs links for menus now go to base url
(#716) - Preparing ground by at least being in session consistent