TapQueue server and station 0.13.0

Added

• Check for updates for clients and stations, on the console's Updates page. It asks GitHub
  for the newest client release, or the station build that goes with this server (never a newer
  one), and Publish has the server download it, check it against the release's SHA256SUMS
  and hand it out, so PCs and stations update without anyone downloading and uploading programs.
  tapqueue-admin clients update and tapqueue-admin stations update do the same; --check only
  looks. Needs the server to reach api.github.com and github.com, and the same role as
  publishing a build by upload (admin of Updates). Uploading a build still works.