Filtering in Django admin for various ClientConfiguration models

+ This commit addresses: https://www.pivotaltracker.com/story/show/26464751
+ Creating proxy models for each type of ClientConfiguration
+ Creating custom managers for each proxy model
+ Moving all managers out of models.py and into their own module
Merge pull request #2 from syncopated/master

Add filtering in Django admin for various types of ClientConfiguration models
Merge branch 'master' into develop