Add CONTEXT_ROOT setting for wsdl service location rewrites

[MeFisto94]

Is your feature request related to a problem? Please describe.
When castlemock is running behind a load balancer/reverse proxy, it tends to replace the <service> tag at the ?wsdl endpoint with URLs starting like localhost:8082, which then are not useable by the client at all (obviously, localhost is almost always wrong).

Describe the solution you'd like
Since it may be non-trivial for castlemock to figure out the correct root itself, a simple environment variable to define the base/context root may be sufficient enough

Describe alternatives you've considered
Parse web requests to inspect Host/Location headers both in the case of the wsdl call (that would even support multiple roots), or somehow from the Web UI and storing it. That doesn't seem as good, though.