Add timezone support

Summary:
Allows user-configurable timezones. Adds a preference panel, and migrates to the
new date rendering in easily-modified areas of the code. ***In progress***.

Test Plan:
Check database to make sure the field is being changed when the settings are
changed; check affected views to see how they render times.

Reviewed By: epriestley
Reviewers: epriestley
CC: aran, epriestley, toulouse
Differential Revision: 475

resources/sql/patches/045.timezone.sql

@@ -0,0 +1,2 @@
+ALTER TABLE phabricator_user.user
+  ADD timezoneIdentifier varchar(255) NOT NULL DEFAULT "America/Los_Angeles";