Configurable Tree layout

Adds a little optional panel to adjust the tree layout on the fly.

Not pretty, I am truly ashamed (far too much use of the $compile function...), but just to get the point across.

We want even more in the future and change algorithms that determine the tree nesting, which might be a little trickier and therefore won't be done too soon.

Mind that using the input forms to manage node separation and the like are not safe to use. Not sure, could be a bug in dagre. The +/- buttons do work, as well as using predefined settings for a compact or a wide tree.

Changing direction also works, which is, even if a little radical, quite an interesting experiment.