ENH: Working prototype of add_to_canvas behavior for query_dict

@NSLS-II/development-team Here is a working prototype of the desired behavior in VisTrails when a user wants to add their scan to a VisTrails canvas. See `example_vistrails/add_to_canvas_brokerquery.vt`.  That .vt file currently requires that you be on one of the computers at CSX with the devel branch on metadataStore installed.  I will continue to update this as I make progress, but have a look.
This could end up being `data_dict[None]` which I don't think will do what we want.  I think we also need to always return a list.
```
keys, data = zip(*six.iteritems(data_dict))
```
will do what we want here