dropdown widget to replace current non functional analyze/visualize/expo...

...rt dropdowns

This widget just takes a list of links and emits a navigate event for them, using the bootstrap dropdown, and keeps track of what is active.
If this looks ok to you, i will improve it by showing on the button the active view, then removing it when the view is closed.
i don't know (yet) how, but we'll have to come up with some flexible registry for these