Staff role-based access to providers allowing multiple practices

Assigning a staff user to a provider node (from admin/users) will allow the user to only see providers under that provider node's tree. 

This allows the same instance of popHealth to be used by multiple practices through separate staff user accounts.

*This feature is a precursor for the 'aggregate measure' feature implementation, allowing one practice to compare their measure percentage with the respective aggregate percentage in the system.