Session and model management issues
This MR
- changes the default session name from "session ###" to "session type models" (where session type is "polygon", "discrete", etc.);
- fixes the way sessions are closed (so that model entities are properly removed);
- renames models with default names when exporting to an SMTK file;
- does not include model names in entity names when assigning default names; and
- fixes/removes many superfluous debug/warning/informational printouts.
See CAM issue 174 for more information.