X:line propagation

This PR implements what is needed to propagate X:lines to the other servers in the network when an oper adds or removes them, as well as during a server burst.
You have nothing in this function that propagates the ADDLINE.

You call the addxline action, which is implemented by x:line modules to add the x:line to the local server's data.  It's not forwarded on, however, and as a result, only the local server and the remote servers one hop away will ever find out about this.  The larger network will remain fully unaware.

In the Desert Bus style setup, this means that an x:line will only ever be seen by one user server (because the only server one hop away is the hub which doesn't have client ports).