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.
maybe something we need to decide on. I'm personally not a big fan of inheritance and would say at this point, composition would suite better, since observables.Observable just extends the Service and not the other way around. but this is just personal opinion and Johannes might have another one :)