Moved the undo and redo functions to the document ns. Fixed bug when redo/undoing at the end, beginning or with an emtpy history.
Preliminary implementation of undo.
Moved protocol to the unused lab.model.protocols ns. Implemented the Text protocol fot the text editor component. Defined the undoable text operations based on this protocol's functions.
Implemented the rest of the functions from the Text protocol for UIComponent and JTextPane.
Removed the call the highlight on each undo/redo, let the highlight shceme decide what to do.