Requirements: use stable version of django-debug-toolbar

Per evernote@2660327
Cleanup: removed dead template filter
Cleanup: Use render() instead of render_to_response()
Cleanup: Get rid of __future__.absolute_import imports

Despite what the docs say, this is available from 2.6 onwards.
djblets: Use json instead of simplejson
Cleanup: Remove pootle_misc.redirect

All it does is what django.shortcuts.redirect does, with unused extras
Cleanup: Prefer redirect() over HttpResponseRedirect
captcha: Simplify the regex
util: Drop unused imports
translationproject/views: Make the import block more readable