Add travis support and fix audio and video tags

- Update image test following code change:
  HTML for images with thumbnail that's not for pdf has been changed in https://github.com/Connexions/rhaptos.cnxmlutils/pull/44 but one of the tests wasn't updated

- Add travis support
  Should we also run the tests in manual-tests?  I haven't tried running them yet so I'm not sure why they're manual...

- Add controls="controls" when generating audio and video tags

- Discard src attribute from audio and video tags (using &lt;source&gt; tag instead)