Remove ClickHandler for ModelTree

The click event is handled by the ComponentCell.
Strip drag-and-drop event handling from ModelTree

Drag-and-drop functionality is obsoleted by the ComponentCell.
Replace ModelCell with ComponentCell on initialization of ModelTree
Add enclosingTreeItem member to ComponentCell

As with the ModelCell, the ComponentCell needs to know where it is in
the ModelTree.
Add port-counting methods to ComponentJSO

Also deprecate goofy #getPortsProvided and #getPortsUsed in favor of
#getProvidesPorts and #getUsesPorts.
Add new components to ModelTree

Still need to handle:

- "linked" components
- actions on the components
- filtering "provides" components

Deprecated methods that added ModelCells to the ModelTree.
Experiment with CSS for ModelTree