Switch to Jest-style reporter

[developit]

This will make it much easier for folks who switch between the two tools.

[suchipi]

I hacked one together a while ago: https://github.com/suchipi/karmatic-nightmare/blob/master/src/jest-style-reporter.js

It's not the same as what jest uses, but it has the same look-and-feel. We might be able to use what jest uses, though; I'd have to look into it.