Experiment with canPublish() and auto-restart

We currently launch the devappserver with _automatic-restart=false_ as making changes to a class when debugging causes the server to be restarted and thus terminates the debug session, which is very frustrating (#836).

But _automatic-restart=false_ also leads to some puzzling behaviour as changes to non-class files are eventually published and picked up by the server, but changes to class files are not (#1428).

We may be able to leverage the `ServerBehaviourDelegate#canPublish()` to check the launch's mode (i.e., are we in debug) and if any of the launches debug-targets or processes are currently suspended.