GitLab

Summary:
Adds stratified sampling of sequences within categories applied after category / sequence filters but before the num sequence limit.
It respects the insertion order into the sequence_annots table, i.e. takes top N sequences within each category.

Reviewed By: bottler

Differential Revision: D46724002

fbshipit-source-id: 597cb2a795c3f3bc07f838fc51b4e95a4f981ad3