Move HWI out to Github

I have seen HWI cause a number of build and test errors, and it's now going to cost us some extra work for integration with security. We've worked on hundreds of clusters at Cloudera and I've never seen anyone use HWI. With the Beeswax UI available in Hue, it's unlikely that anyone would prefer to stick with HWI. I think it's time to move it out to Github.