Update the template loading/rendering code

[mjumbewu]

Django 1.5 made various updates to the template rendering code to make it compatible with Python 3. Mimic those changes in Djangobars so that it's also compatible with Python 3.

The changes will be found in:

• The template response class (djangobars.template vs. django.template)
• The app_directories template loader (djangobars.template vs django.template)

This is a pretty straightforward issue as it mostly involves mimicking the Django, but it's a good way to learn a bit about the internals of both Djangobars and Django.

UPDATE (2015-01-08): This task is still relevant, but moving forward it must also keep an eye on DEP 182: Multiple Template Engines.