Fixes 902142 - adds support for partitioning matviews

* Includes a migration that drops foreign keys on
  parent signature_summary tables
* Downgrade restores the FKs
* Also runs backfill_weekly_partitions() for signature_summary tables
Merge pull request #1390 from selenamarie/bug902142-partitioning-for-matviews

Fixes 902142 - adds support for partitioning matviews