(TK-33) Add redirect support to proxying

This PR adds proper redirect support to proxying in the Jetty9 service. 
Could you make this configurable? I don't care what the default would be, but for the TK proxy to work correctly I need to deliver the redirection headers back to the browser to handle the unauthenticated state. I admin that currently it's a kind of a hack but without the "middleware" support I don't have any other chance than that.