provide undo capability for additions

[abargnesi]

The following Undo/Redo actions should be supported:

• [ ] Undo: Expand All Edges ***
• [ ] Undo: Link to Knowledge Network
• [ ] Undo: Expand Neighborhood
• [ ] Undo: Added Nodes
• [ ] Undo: From Knowledge Network

*\ rename Expand Node to Expand All Edges

Cytoscape provides the following classes to help with this:

• UndoSupport
• AbstractCyEdit

raise by @ncatlett