Changes to the Core suggested by DV Issue 24

1. Removed the Roles entity from the Core schema
2. Renamed ActionPeople to ActionBy
3. Changed RoleID to RoleDescription in the ActionBy entity.
I think we don't want to control the values people put in their
descriptions of Roles that people play in Actions, so I changed RoleID
to RoleDescription rather than RoleCV.

Any objections?