tube-stream: add tube-offered signal
tube-stream: add tube-offered signal

community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble