Vistrails integration

Added display_dict widget to display a nested dictionary

Added a generic query widget that acts as a front end for the data broker and uses display_dict to show the results from the data broker.  This widget could be used as a template for any query/result

This may not be entirely ready to be merged into master, but it should at least be on everyone's radar as I will not be working on it for the next 5 days
Sorry for the spam, changed my mind about the other comments.  This connection should be done in the `__init__`, `self._search_fun` should default to `None` and `search` short-circuits as a no-op if `self._search_fun is None`.

We should also be clever and disable the search button if there isn't a valid search function registered.