Testing of the dataprovider, interfaces, etc.

[andersx]

I updated the repo with continuous integration testing via TravisCI: https://travis-ci.org/qmlcode/qml-interface
I added all the test from my old QML repository, and made sure building and testing works for Python2 and Python3.

Not sure how or if we should write tests for the interfaces. Keeping this issue open until we have a more set version if the model classes and dataproviders, and proper testing of those.