Receive undo/redo actions from CODAP
Receive undo/redo actions from CODAP

When undo/redo is received, we simply use our own undo history stack to
perform undo and redo.

This calls undo/redo on the link-manager, following the pattern of the
app-view.

concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models