Add db index for MessageModel and PVModel

[Bill-Becker]

This is the SQL translated from django's migration file for the two db tables:

BEGIN;
--
-- Alter index_together for messagemodel (1 constraint(s))
--
CREATE INDEX "reo_messagemodel_run_uuid_f98c3013_idx" ON "reo_messagemodel" ("run_uuid");
--
-- Alter index_together for pvmodel (1 constraint(s))
--
CREATE INDEX "reo_pvmodel_run_uuid_ffc792f5_idx" ON "reo_pvmodel" ("run_uuid");
COMMIT;

[GUI]

I'm obviously not super familiar with the Django side of this, but that SQL looks right, so this looks good to me, and I think these indices will help with some of the production load. Thanks!