Refactor RecruiterSubmissionRecordFilterer spec.

Refactor RecruiterSubmissionRecordFilterer#initialize to only take a Recruiter.
Rename #jobseekers to #jobseekers_in, as it now takes a SubmissionRecordList.

Subsequent such refactorings will make it trivial to chain Filterers.
Fulfill refactored RecruiterSubmissionRecordFilterer spec.
Refactor DateSubmissionRecordFilterer spec.

Refactor DateSubmissionRecordFilterer#initialize to only take a Date.
Rename #jobseekers to #jobseekers_in, as it now takes a SubmissionRecordList.

Subsequent such refactorings will make it trivial to chain Filterers.
Fulfill refactored DateSubmissionRecordFilterer spec.
Add very preliminary specs for CombinedFilterer.
Add spec for RecruiterSubmissionRecordFilterer#as_filtered.
Fulfill spec for RecruiterSubmissionRecordFilterer#as_filtered.
Add spec for DateSubmissionRecordFilterer#as_filtered.
Fulfill spec for DateSubmissionRecordFilterer#as_filtered.
Fulfill spec for CombinedFilterer#jobseekers_in.