Bug 1008447: Add CachingMixin and CacheManager to User class.

When a new link is created, the cached results for a user’s links
doesn’t get invalidated because, while the link has a foreign key to the
user, the user isn’t cached by django-cache-machine. By adding the mixin
and manager to the user class, when a new link is created, the user, and
thus it’s related links, should be invalidated, fixing the caching 
issues on the dashboard.
Avoid count query in stats display to avoid caching.

Since all the pages the stats are included on already use the user’s
link_set, the results are cached (yet up to date due to invalidation) 
and don’t add any queries.
Add New Relic code to WSGI file.
Styling for old versions of IE
Bug 1005946: Ignore links that point to nonexistent users.
Add temporary command to deploy script to run via chief.
Remove temporary command from deploy script.
Do not run prime_app anymore, it should be unnecessary.
Fix the manager for Category and fix the validation.

The manager for Category now inherits from CachingManager and 
MPTTManager, whereas before it was only using CachingManager, causing
MPTT-related things to fail.

The validation now accounts for edge cases it previously missed, such as
assigning a parent to category that already has children or assigning
a parent that is not a root node. Previous reliance on get_level failed
when parents were assigned but the new level hadn’t been computed yet.