Travis CI

 * Add travis yaml
 * Update README with link to travis ci
 * Make ENV vars global
 * Add rake dependency to Gemfile test section
 * Add default rake task for running tests
 * Add database.example.yml so it can be copied to database.yml when Travis CI builds the app
 * Add before_script block to create a test database and database.yml
 * Before building:
   * Migrate
   * Prepare the test database