Start work on History window.
Fixes #195.
History window available through main window.
Types for commands, history items, etc.
Working on #202.
Working on #202.
Add module removed message.
Set better minimum size.
Simplify HistoryItem toward Memento pattern.
History window displays xml memento for add/remove module.
Start TDD on HistoryManager.
Push module position info down to engine layer.
Underlying HistoryManager done.
History Window buttons enabled w/GUI behavior, no action yet
History Window works! Next: add/remove connection undo/redo