IDE protocol should have means to notify DCP that the IDE endpoint is shutting down

Currently there is no good way for the IDE endpoint server to tell DCP that it (the server) is shutting down and thus no new requrest should be made. A scenario where this is useful is when the IDE is closed during application run. In the current implementation DCP will try to reconnect if the IDE connection fails, resulting in spurious errors.

A simple solution is to have a dedicated notification type that tells DCP the endpoint is shutting down.