(TK-33) Add redirect support to proxying

This PR adds proper redirect support to proxying in the Jetty9 service. 
@fhrbek we've been having a discussion about the best way to handle redirects.  The approach that @praxxis and I were espousing was to munge the location header, as I believe that you are suggesting.  However, that was proving somewhat problematic to implement, so we decided to go this route for now; we were expecting to come back around later and add an alternate implementation based on the location header, and config settings to allow you to choose between these behaviors.  Perhaps we need a config setting now though.

@fpringvaldsen @camlow325 another thing to keep in mind is that if @fhrbek has one set of needs/requirements for his proxy route, and some other burgundy app has a different set of requirements, then this config setting can't be global.  It has to be per-proxy-instance.  :(