Add repro SIP proxy module.

Currently requires using a web interface to set domains and register users, and also requires restarting the service after setting the domain. There's an issue with /repro being redirected incorrectly by the admin interface, so you have to go to a specific page like /repro/domains.html.

I've tested voice calls between 2 users on the box with Jitsi, Empathy, and CSipSimple. I didn't test with users on different servers.