Add Travis-CI configuration for running the tests

You can see the latest result here: https://travis-ci.org/davehunt/mozdownload/builds/10417725

We may want to use a different e-mail address for notifications. What do you think @whimboo? At the moment I configured it to use the same as mozbase.

At the moment, the IRC notifications will not work due to https://github.com/travis-ci/travis-ci/issues/436