Initial implementation of pjax partial page rendering for great performance justice

There is something really weird happening with /edit/ links and (as far as I can tell)
only edit links, so pjax on edit links is disabled for now.

I consider skipping /edit links to be a hack. Please don't merge this unless you're comfortable with such insanity ending up in the codebase. (Though if the reason for the breakage is obvious to you, tell me and I'll fix it up)