Fix for TIM-449. Do not use Peer UUID

@wedaly @ormsbee 

This is a temporary solution to resolve issues with using the Peer Submission UUID. Now create_assessment() will use the scorer's submission_uuid to look up all relevant information about the assessment. This requires more queries, which is unfortunate, but does drop one of our more expensive queries in "_get_latest_workflow()"

Tests all pass; I intend on doing a bit of click testing in the morning as well.