Highlight update time in revision list

Summary:
This is another experiment for reducing reviewers response time.
I stole the idea (and colors) from [[ http://www.reviewboard.org/media/screenshots/2009/02/02/dashboard.png | ReviewBoard ]].
I actually quite like it (except when everything is red) and I can image that people will review just to have better color balance.

The code is not production ready for these reasons:

- We load holidays again and again for each revision. I couldn't cache it to static variable because it could persist multiple requests, right?
- I don't know how to expand height to the whole cell (I'm really bad in CSS).
- CSS rules are probably in wrong file.
- We probably want to use different colors.

This is how it looks:
{F16406}

Test Plan: Displayed revision list.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3190

scripts/celerity_mapper.php

@@ -90,6 +90,7 @@ $package_spec = array(
     'differential-changeset-view-css',
     'differential-results-table-css',
     'differential-revision-history-css',
+    'differential-revision-list-css',
     'differential-table-of-contents-css',
     'differential-revision-comment-css',
     'differential-revision-add-comment-css',