Python26 cleanup

I previously made two changes that made the develop branch incompatible with Python 2.6:
* collections.OrderedDict is unavailable in Python 2.6
* datetime.timedelta has no total_seconds method

In order to compensate, I've made the following changes:
* Include newer collections.py in our python_packages, which contains OrderedDict
* Implement a more generic datediff function, with a "units" parameter that allows output as seconds, hours, days, etc

In addition, this contains a few small updates:
* Use settings.LOG instead of logging module directly (funnels everything through a specific logger, easier for internal and external apps selectively turning on/off debug information)
* Avoid dynatree css file generating any 404s by removing cruft