Update copyright
Gather lock counts for the current db

Tag with lock mode and table name (though indices will show up here
as well).
Add bgwriter stats
Merge from master

Conflicts:
	checks.d/postgres.py
Add a test for bgwriter and lock collection
Update tests with new bgwriter stats.

Locks require scaffolding to test. May consider afterwards
Merge pull request #1019 from DataDog/alq/pg-locks

Postgres locks per mode and thing locked