Chrome for Diffs

Site-wide changes
* Instead of running the View class of main content, use template inclusion
* To aid that, add a template tag that alters context scope within a template
* Move drawer content into chrome.html so that the TOC and Versions tabs can be "blocked" out
* "Block" out TOC, Versions tab, secondary header (effective date)
* Add (terribly looking) version comparison selection interface

Diff specific:
* Fix bug where full section wasn't displayed when diff adds a new section
* Diff TOC links to other sections in diff mode; also indicates if this section was added, modified, or deleted; TOC includes sections from both versions of the reg
* Diff Versions tab has a link to turn off diff mode, as well as an indication of which versions are being compared
* Turn of JS interactions for TOC and versions tab when in diff view
* Effective date includes both versions
* Redirection url for use with the version comparison selection interface