Phame - fix some issues with feed reported on github (290, 291)

Summary: we need a link with type=self to pass xml validation. Note we will always fail validation until we remove any sigil-related stuff from the resultant HTML since we just made that up for our purposes. Also serves up the feed link on the blog view controller, complete with tooltip about how the custom domain stuff isn't supported.

Test Plan: viewed a blog page and liked the feed uri property. viewed a feed and verified the new link self stuff. post push I'll try the validator again.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, vrana

Differential Revision: https://secure.phabricator.com/D5667