Travis-CI badge that shows the continuous integration test status, closes #1.

I made a few changes, most notably:

- I modified the `database.yml` test environment to play nicely with Travis-CI.
  - Travis-CI requires the database user to be named `postgres`.
- I added the `test_unit` framework back in, this can be replaced later by another framework.
- I added a sample `PagesController` test to test access to the about page.
- I added `.DS_Store` to the `.gitignore` file to avoid adding Mac OS files to the repository.

Feel free to merge if everything looks good (the "test" is passing).

Thanks!