LUN-827 Make use of the new admin extending app
LUN-827 Organize imports
LUN-827 Provide both the name of the field and the related manager
LUN-827 Removed unused import
Fixed typo
Removed version number for python-graph-core from deps links.
Merge remote-tracking branch 'origin/master' into LUN-827

Fixed conflicts:
	setup.py
Merge pull request #16 from pbs/LUN-827

LUN-827 -- Rewrite admin extensions based on the new django-admin-extend app
Merge remote-tracking branch 'origin/master' into LUN-718

Fixed conflicts:
	cms_templates/admin.py
	settings_test.py
LUN-718: changed validation messsages.
Fixed the way PLUGIN_TEMPLATE_REFERENCES setting is loaded.