Store isolate in name and groups registries only once
New heartbeat discovery handling

- Send a signal using the HTTP transport with multicast information as 'extra' and with the local peer dump as content
-> handle the received signal to register the remote peer.
Java Herald directory acts like Python one about peer registration

- Store peer only once (name and groups)
- Notify about peer registration only once
Better handling of the no-extra, no-peer case in HTTPTransport
Same heartbeat handling as in Python -- Causes dead locks :(
Moved regex compilations outside locks
Herald Java implementation uses the same locks as Python one

 This removes a lot of possible dead locks
HTTPAccess: support port loaded as String
Use constants for HTTP discovery message subjects
Corrected peer update/registration check in core Directory -_-'