adding explicit django_debug_toolbar configuration, http://git.io/rouj9w

Please see: https://github.com/brainstorm/biostar-central/issues/22
Problem Using Django==1.6.2 and django_debug_toolbar > 0.11.0 .

Aditionally I think is a great idea and best practice define the packages version in the requirements.txt. I will write this like an enhancement.