Watches should not try to reconnect when a project has been deleted

When a project has been deleted from the webconsole, the watchmanager in eclipse is not notified. Each watch that times out tries to reconnect to some of the dead project's urls. Each access is rejected with 403 errors (the project could exist but not be visible to the user).
After each attempt, the watches will wait a little longer before trying to reconnect, until it eventually stops trying.

Since the watch manager has access to the projects, it can try to check the project exists before connecting the watch