Modified routing and favicons

This standardizes on .ICO favicons in the root of the site. Also cleanup of routes.py files, both the app routes in webapp/ and the template for site-wide routing (SITE.routes.py).

I removed the "overrides" of BASE router in webapp/routes.py, since it turns out this doesn't work! I moved the critical stuff (mostly just explicit use of default routing) to SITE.routes.py where it belongs.