Ignore the database.yml

* everyone has their own database.yml e.g. own username/password
  or some don't have a PW at all (for my my user account handles
  that kind of)
* provide a database.yml.example as a guideline that people
  can use
* use postgres for tests and production as well (was sqlite before)
Merge pull request #3 from PragTob/database_config_fix

Ignore the database.yml