Django 1.5: used the receiver decorator

Mostly syntactic sugar to allow connecting various signals to the same
handler. Other signal handlers have been left intact.

Fixes evernote#176.

Conflicts:
	pootle/apps/pootle_project/models.py

Cherry-Picked-From: 97eea7338c36678f2eadd2656f239efeb4eada24
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
Tests: Revert tests that break on mysql (sigh)