Add multi-tenant functionality

To supplement multi-source functionality, we should add explicit multi-tenant functionality similar to hibernate - http://docs.jboss.org/hibernate/orm/4.2/devguide/en-US/html/ch16.html

This would mostly be carried out at the datasource level, but would also make us cache aware. Otherwise our current story is to implement multi-source and add row level filters to all multi-source tables to prune based upon the user - which we could choose to expand on in Designer or the server such that the necessary roles are created automatically.