Use push helpers to format Talker messages
Use push helpers to format Talker messages

This correctly shows the actual pusher when a push happens instead of
whomever committed the last commit. It will also make the message a tad
more interesting:

  Joe Pusher created some-branch from master (+2 new commits)

instead of

  Mary Committer pushed 2 commits
parshap/github-services,DataDog/github-services,Seldaek/github-services,espace/github-services,1234-/github-services,illan/github-services,Jdesk/github-services,Zarthus/github-services,stof/github-services,galeksandrp/github-services,supriyantomaftuh/github-services,YOTOV-LIMITED/github-services,rkh/github-services,apiaryio/github-services,leah/github-services,dataRonin/github-services,Zarthus/github-services,adrianschroeter/github-services,VladRassokhin/github-services,dataRonin/github-services,espace/github-services,parshap/github-services,netlify/github-services,solanolabs/github-services,brntbeer/github-services,Jdesk/github-services,Mumakil/github-services,myget/github-services,guardian/github-services,stof/github-services,myget/github-services,projectkudu/github-services,projectkudu/github-services,Seldaek/github-services,elordahl/github-services,pkdevbox/github-services,brntbeer/github-services,headius/github-services,supriyantomaftuh/github-services,adrianschroeter/github-services,netlify/github-services,YOTOV-LIMITED/github-services,travis-ci/github-services,galeksandrp/github-services,guardian/github-services,wassemgtk/github-services,DataDog/github-services,1234-/github-services,apiaryio/github-services,Mumakil/github-services,KamranMackey/github-services,solanolabs/github-services,timabbott/github-services,github/github-services,pkdevbox/github-services,github/github-services,wassemgtk/github-services,travis-ci/github-services,VladRassokhin/github-services,timabbott/github-services,headius/github-services,elordahl/github-services,marko-asplund/github-services,KamranMackey/github-services,illan/github-services