Add preliminary specs for JobSubmissionRecordFilterer.
Reduce specs for JobSubmissionRecordFilterer to a single, more manageable one.
Fulfill preliminary spec for JobSubmissionRecorderFilterer.

Add #for_job? to Posting, Submission, and SubmissionRecord.
Expand the #before step of the JobSubmissionRecordFilterer spec, in anticipation of adding specs for #jobseekers_in.
Add specs for JobSubmissionRecordFilterer#jobseekers_in.
Fulfill specs for JobSubmissionRecordFilterer#jobseekers_in.
Add (fulfilled) spec testing the inclusion of JobSubmissionRecordFilterer in a CompositeFilterer.