added 'created' to all tokens and 'generation' to accounts

This doesn't actually do anything with the timestamps, it just brings them into existence. The 'generation' on accounts isn't *necessarily* for [this proposal](https://mail.mozilla.org/pipermail/sync-dev/2014-January/000664.html) but it could be used for that; I was specifically thinking about https://github.com/mozilla/fxa-auth-server/issues/388#issuecomment-30184875

While I was at it I did a minor refactor to pull all of the sql statements up a notch. Also, it turns out that `db_tests.js` was totally busted and would silently always use `heap.js`. :banana: 

Lots more work to do in this area, but this is mergeable, so r?

P.S. bigint for timestamps, yea or nay?