Add travis config and modify tests so they work on Travis CI

This branch hooks up tests with Travis CI service (https://travis-ci.org). To automatically run tests on every push you need to enable Github Travis CI hook after you merge this pull request into master.

You can see example Travis test run at https://travis-ci.org/Kami/python-video-converter/jobs/8851155

Keep in mind that tests in master currently fail, but I've fixed this in #14.