mojo: Use HTTP instead of unix socket, add way to find right port.

Unix sockets are nice (especially since they can be at a well-known
location in the filesystem) but they're harder to use with WebSockets
from Qt and that is likely the path we want to go to avoid trying to
reinvent long-polling and such.

To make it possible to find the status server at a random TCP port, use
a well-known location (with a proper name this time) to point to the
right URL.