Improve testing harness

[sudara]

We are currently testing by confirming events are fired by reading log lines. Move to a visually improved html test page which responds to events directly and visual elements turn green when tests passes.

I liked how qunit feels:

However, in our case, we need to interact with the DOM to trigger most of the tests we care about properly (did playback succeed, is the next track triggered, etc). So although we could move to some amount of unit tests (for cases where it makes sense to test code in isolation), we are still "doomed" to having a custom page to run selenium against.