Travis ci for upstream

This pull request will enable Travis CI integration on the open-avb-next branch.

You can see how it works by looking at [my travis-ci branch](https://github.com/pinealservo/Open-AVB/tree/travis-ci) and observing the build status image link in the README area. Click on it to go to the Travis CI site, which will show detailed build information.

When the pull request is accepted, I will flip the switch on Travis CI's configuration page for the AVnu/Open-AVB repository and we should get a 'build passed' image on the `open-avb-next` page.