LUN-827 Make use of the new django-admin-extend
LUN-827 Provide both the name of the field and the related manager
Fixed typo
Fixed dependencies.
Since this is a public project, it shouldn't depend on our forked
django-cms version.
Merge pull request #27 from pbs/LUN-827

LUN-827 -- Rewrite admin extensions based on the new django-admin-extend app