ServerConnection

Registers a listener for updates from the model. A listener is simply a partial function which receives instances of U. Therefore the listener can decide with pattern match cases which updates it wants to handle.

Example:

 m.addListener {
   case NcviewSync.Open(path) => ...
 }

Note: If the listener should be removed at some point, it is important to store it somewhere:

 val l: NcviewSync.Listener = { case NcviewSync.Open(path) => ... }
 m.addListener(l)
 ...
 m.removeListener(l)

Un-registers a listener for updates from the model.