Configuring the Template Attribute Resolver to consult its dependencies.

[Cantor, Scott]

> Why would it need to be a List? I don't think that's true, there's just a goofy V2
> feature using that assumption to build a template if one isn't provided, which I
> don't think is really a necessary feature.

Specifically (this is what I put in the JIRA issue that's tracking stuff we meant to deprecate but forgot to), I think we meant to deprecate the option to omit <Template> from that plugin type since that's pretty weird and silly as a feature.

The only advantage to trying to do anything about it now is if we decided to "rush" the removal of that implicit Template feature in V4, and if we did that, we would leave SourceAttribute in the schema but ignore it, so it could be removed by deployers and eliminate that duplicative need to list all the source attributes twice (and it would be yanked in V5 from the schema to close the book on it).

-- Scott