Localhost port numbers should be configurable (currently fixed to 8080 and 2023)

[mpsrig]

I have systems which already use these ports (especially 8080).
As the RIPE Atlas software is only opening these ports on localhost, for what seems to be some form of inter-process communication, it seems the choice of port number is arbitrary, and should be configurable by the system administrator.

(Alternatively, something like UNIX sockets could be used instead for the IPC, to avoid consuming a port)

[AtlasMUC]

This is already supported, just not documented. See PR#92.