Start using a db in the cloud for dev; #415

Rather than requiring a local Postgres instance in order to stand up
Gittip, this connects to a db in the cloud (a free plan from Heroku
Postgres). The plan is to reset this database in the cloud every six
hours or something, populated with fake data. That way people can get
started hacking on Gittip more easierly.

For running tests we should use postgression.com for ephemeral,
single-use databases.