Persist resource across sessions

This was somehow lost once we implemented random resource strings
Although its good that initally a random resource is chosen, it
still should persist across sessions.

This helps to kill zombie client connections on the server because
most servers kill the old session once a new with the same resource
connects

Also dont notify the user about resource conflicts if no custom
resource is set. We should not expect users to know about resources
and what they are used for as long as possible.