Implement Undo

[jenslincke]

Lively2 came with default UNDO support from the browser, so we did not port our own UNDO layer. Since, syntax highlighting seems to break undo, and a general undo would be need I think we should do our own UNDO / REDO history again.

We should start with text, but normal morphic interaction, like moving and deleting object manually should be covered by undo....

Who want's to help?

[jenslincke]

 http://www.lively-kernel.org/repository/webwerkstatt/issues/120125_LivelyUNDO.xhtml

[fbo]

If this is done right and we eventually get to having command objects that can also be serialized and sent over the network, then that would be super useful for quite a bunch of things :).

I would like to have a look at this, too.