Add javelin_tag(), convert easy callsites
Summary:
- Implements javelin_tag(), which is javelin_render_tag() on top of phutil_tag() instead of phutil_render_tag().
- Manually converts all or almost all of the trivial callsites.
Test Plan:
- Site does not seem any more broken than before.
Reviewers: vrana
Reviewed By: vrana
CC: aran
Differential Revision: https://secure.phabricator.com/D4639