Add a little SQL-info script that is sort of useful maybe?

Summary: I'm not aware of an easy way to get this information through normal tools. I'm sure there's some fancy GUI client that has it but this seems worth keeping around.

Test Plan: ran script, got helpful information about data sizes

Reviewers: nh, btrahan

Reviewed By: nh

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1916