Update django-debug-toolbar to a version above 1.1

Version 1.1 has an issue with jquery: it's not using its own version, and our
current version (1.6.4) doesn't have ```$(...).on()```.

The latest version on trunk has it all though, so as soon as version 1.2 (or
above) is released, we'll be able to use it instead of the github version.