Provide option to disable CoAP and/or HTTP interface

[mmccool]

Maybe (eg for security reasons) I don't want to run the service over CoAP, or over HTTP (eg just one of the two). There should be a documented way to disable each interface (perhaps by assigning a port of 0).

A workaround exists: run inside a firewall and block those ports. But it would be better to have the option to not start them at the source in the first place.

Note as well that if HTTPS (or CoAPS) is added, I may still want to run an HTTP or CoAP interface in parallel. The reason is that I may have local processes running on the same computer (eg inside the firewall) and don't want to have to fuss with certificates etc (which may be broken anyway in the case the device is temporarily offline). In this case I might open the HTTPS port to the outside but block the HTTP port using the firewall so it is only accessible to internal processes. I might also do this on a local network and block external access to HTTP using the NAT firewall.

So in the long run the system may have four separate network interfaces (CoAP, CoAPS, HTTP, HTTPS) and I would like to selectively enable and disable each one.