pg_stat_statements on PostgreSQL

Except slow queries, pg_stat_statements gives us information about all queries and how many times it is executes along with total runtime, disk usage.

PostgreSQL version 9.5 also has information about max, mean, min time of execution for query.

For 9.2 - https://www.postgresql.org/docs/9.2/static/pgstatstatements.html

For 9.5 - https://www.postgresql.org/docs/9.5/static/pgstatstatements.html

Also it may be useful for performance.

/cc @pcarranza @yorickpeterse @northrup @jacobvosmaer-gitlab @pacoguzman @eReGeBe