ModelBuilder: Add keybinding to ```smtk::model::DeleteMeshOperator```
Once the smtk delete mesh collection operator has been added ( see smtk#29 (closed) ) we need to allow the user to an easy way to access this operator.
The best way would to construct a smart delete operation and bind it to the delete key press. This would than check to see what items are currently highlighted and perform a
delete operation on each.