Create base template. Index extends base

-  Create base.html template with template blocks for top nav, left nav, body, footer, and postcontainer to allow adding pages with left nav, top nav, footer in common with index.html
-- Create leftnav.html, topnav.html in new templates/nav directory
-- Modify index.html to extend from new base.html.  Calendar moved to body block, calendar scripting moved to postcontainer block