implemented named roles for permissions system. %userRoles maps role
names to numeric permission levels, and %permissionLevels now maps
activities* to role names. A slight change to Authz.pm accompanies this
change to do the role-to-permission-level lookups.
* a.k.a. operations, privilegespermissions, gotta get the terminology
straight. think of the users!
%userRoles should be used by modules such as UserList for providing more
intelligent editing of the permission_level field. Another possible use
would be to for pretty-printing user types -- a user could be called a
student, ta, professor, etc. based on what role corresponded to their