Better to use filenames which are commonly used in the python word then
custom ones.

underscore as separator.
Changed setup of functional test in dashboard/communication to be passed
with code populated from name.

This allows updating code in both places, if necessary. Getting Django
1.5 support would be painful otherwise. This also removes the circular
dependency of django-oscar-testsupport on Oscar.

The requirements were merged. The imports were updated
accordingly. Unused imports in the touched files were removed. No
further changes.

Fixes #376

This allows admins to:

* Preview emails in the dashboard
* Send preview emails
* Save emails

Fixes #359