[#570] Replace django.views.generic.simple.direct_to_template()

direct_to_template() is being deprecated in Django 1.5 and the
recommended replacement is django.views.generic.TemplateView().
[#570] Remove verify_exists attribute from models.URLField

The varify_exists attribute for models.URLField is being deprecated.
We can get away with just removing our references to it since it is set
to False in all instances in the code.
[#570] Change call signature of dehydrate() in child classes of ApiField

Add the for_list param to ConditionalFullToOneField.dehydrate() and
ConditionalFullToManyField.dehydrate()
[#570] Upgrade most libraries in requirements/2_rsr.txt

As part of our work on upgrading to Django 1.7 we should use the most
modern version of our library dependencies possible. This commit
upgrades most of the deps in 2_rsr.txt.
Merge pull request #571 from akvo/feature/du570_upgrade_python_libs

[#570] upgrade python libs