Add functions to get source references without the descriptions

I didn't like how there wasn't a way to _just_ get source references without the descriptions. The sources query endpoints are awesome when you want the descriptions, but they can be slow and there are situations where you just want the references.

The docs and tests were in this weird state, as if they were first implemented as just getting references but then were augmented later to also return sources but the docs weren't properly updated for couple and childAndParents.

So I renamed the old getSourceRefs functions to be getSourcesQuery functions and then implemented the getSourceRefs functions so that they really only return the source references.

Here's what we have now:

* `getPersonSourceRefs`
* `getPersonSourcesQuery`
* `getCoupleSourceRefs`
* `getCoupleSourcesQuery`
* `getChildAndParentsSourceRefs`
* `getChildAndParentsSourcesQuery`

I haven't updated the jsFiddle examples because I can't really test them until the build is updated.