[#64070560] Users can be classified as developers by admin users

 - Validate the number of developers against the license iff vendor is not 'openchorus'
 - Specify developer on the create and edit users views
 - Display developer badge if user is a developer (as with admin)
 - Fix an existing issue with the DataSourceValidator shared behavior spec and intoduces a
   more generic validates_with to test for use of custom activemodel validators.