PE-2053: Java Servlet support 

I moved the existing example apps around to make room for a polyglot example, then added servlet support to our jetty service & an example app, then touched up docs a bit.

I don't like how the example apps are laid out now and I want to come up with a better solution.  I left that work for a followup PR as I didn't want this one to get too big and it's not necessarily related.