Fixed #16357 - Added navigation buttons to docs footer.

Thanks ncoghlan@ for the suggestion and Markus Magnuson for the patch.
Prepared search form for multiple languages
Allowed update_docs to build non-English doc versions
Replaced simplejson by system json
Made the docs application/templates translatable
Bumped sphinx requirement to 1.2b1

This is required due to several bug fixes related to better
i18n support.
Fixed version selector for english (quickfix).
Use context lang for get_all_doc_versions
Fix minor grammatical issue in draft CoC FAQ.
Dog-fooding staticfiles' static template tag.
Updated a couple of dependencies, like Django and django-registration.
Fixed #20518 -- Use a stripped background when showing a development version of the documentation.
Improved the dev doc warning after feedback from IRC. Refs #20518.
Fixed #20638 -- Scroll a bit further for internal anchor links.
Removed a background image that doesn't exist.
Removed a background image that doesn't exist. Number two.
Use Google's CDN because security.
Enabled cached static files on www, too.
Stopped using an absolute URL in the homepage.css file.
Updated django-push to 0.5