Visualize rev tree

Now you can play with your documents visually. It is possible and quite easy to make document with any history we want (just dblclick node or text, dblclick key/value to edit)
Also: visual improvements.

Drawbacks: writing it without any library to generate html makes the code not so easy to read and not so easy to write. However, I don't think that we are going to have loads of additional functionalities here so I think plain js will be enough here. Right?