Incorporate conservancy_ssl middleware, etc. into main site, now that HTTPS fully supported.

Previously, SSL on sfconservancy.org was supported using a self-signed cert
only to handle the /admin/ portion of the site. Now that SSL is supported
site-wide, and perfectly mirrors the content available via HTTP, the
conservancy_ssl middleware, URLs, and settings are wholly deprecated and
herein removed.

The main site's urls.py now need adjusting to support /admin/, but additional
code is needed in middleware.py to avoid accidentally serving /admin/ via
HTTP instead of HTTPS.

The latter code is untested; hopefully it works "out of the box". :)