v0.7.8-rc.1

Full Changelog

• Attempt to rework the release-tarball-signing stuff
  #438
• ability to specify webrtc audio/video inputs for the lib to request
  #427
• make screen sharing call FF friendly :D
  #434
• Fix race in device list updates
  #431
• WebRTC: Support recvonly for video for those without a webcam
  #424
• Update istanbul to remove minimatch DoS Warning
  #422
• webrtc/call: Make it much less likely that callIds collide locally
  #423
• Automatically complete dummy auth
  #420
• Don't leave the gh-pages branch checked out
  #418