Auto-instantiate the Herald RPC discovery
Added an Herald RS importer/exporter, based on xmlrpclib
Added remote services bundles to the main script
Create empty groups matching local peer's ones in directory

This avoids a KeyError 'unknown group' exception
The Herald core service is provided only if a transport is active

This avoids to try to use the Herald service while nothing can be sent.
An 'internal' core service is available for transport implementations