In GUI builder, add abilitiy to reference concept by source/mapping pair

[mogoodrich]

In the Form Builder GUI, you are able to look up a concept and add it to a form. In the underlying form schema, this concept is referenced by uuid, because that was the only supported way to reference a concept.

Now that we support referenced a concept by source and mapping pair, it would be great for a user to be able to select the a mapping from the list presented in the UI and then have the form builder use that source/mapping pair here: