ensure page primary_category can be cleared
ensure category source can be deselected
Merge pull request #25 from praekelt/feature/issue-25-ensure-fields-can-be-deselected

ensure fields can be deselected
rename migrations to ensure order
pin raven for consistency
allow for custom license text
migration for custom license
show license in the admin
limit to exactly 1 record and make sure we have at least some sort of license specified
Merge branch 'develop' into feature/issue-21-specify-content-license

Conflicts:
	cms/admin.py
Merge branch 'feature/issue-21-specify-content-license' into feature/issue-26-use-elastic-git