Add unit test scaffolding

This is the first in a series of planned commits. My plan is to demostrate how to unit test a legacy WordPress plugin, I've chosen this one to do it. So I'll be writing tests and probably doing some refactoring to show how to write more testable WordPress code. I figured since I'm doing it I should give it back. My plan is to send them in small chunks to help you code review them. If you would rather one big commit then I can do that.

Here I've add the scaffolding for unit testing and the .travis.yml file for travis builds. I've got it running on my fork. Currently the build is broken, I'll try and fix that in the next PR.