First working version of automated execution of notebooks in example folder.

Very WIP... I will work more on this in the next days...

Edit: No longer a WIP.
> Not really. The event infrastructure is isn't well defined in my opinion, maybe besides change notification, but that's not useful in this case.

So, for now, I think we have to use a big timeout... at least until we have some kind of Bokeh "finish" event to use...