Fix all timezone-related issues and warnings.
Review Request #3035 — Created March 31, 2012 and submitted
The timezone improvements that went in only covered some of the cases where timezones were set. Most weren't actually covered, as several fields were using default=datetime.now. This switches these to use django.utils.timezone.now instead. It also switches away from djblets.util.dates.get_tz_aware_utcnow, which does the same thing as Django's and will soon be removed.
Saw that all the warnings from unit tests went away.