Tail remote logs live

Make 'lymph tail' able to connect and disconnect from service and they
come and go, and that by making lymph.core.services.Service class
implement an Observable interface, that the newly introduced class
RemoteTail will use to observe when services get added or removed,
and react by connecting and disconnecting from this later respectively.
Actually that import makes sense for me: storage depends on the framework basics (Interface, Proxy, etc) and may also depend on utilities. That's like importing ``strip_tags`` in a Django project.