API: Prioritize manual submissions when getting next annotation task

[josh-chamberlain]

Context

It's something I'm thinking about talking to the VA folks—they want to submit things they find. If someone goes to the trouble of submitting a manual source, we may want to reward that behavior by annotating it as quickly as possible. It's also more likely to be valid (I suspect) than something any collector would pull in. What do you think about that?

class GetNextURLForAllAnnotationQueryBuilder ...
...
...
        query = query.order_by(
            URLAnnotationCount.total_anno_count.desc(),
            URL.id.asc()

Requirements

• when getting the next annotation task, we should prioritize URLs which have been submitted manually via data-source/create
  • this takes precedent over other prioritization, i.e. "already >0 annotations" and "oldest first"