WIP: Add Steam

[Fohlen]

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• [x] my contribution will be licensed under ZLIB (for code)

This adds the following features:

• [ ] Achievements (25)
  • [x] Global stats for: kills, kpd, edit time
• [x] Workshop support
  • [x] Upload maps
  • ~Save map with config when uploading to the workshop~
  • [x] Set screenshot on upload if screenshot file is found
  • [x] Set workshop title without mapid
  • [x] Move servercontent from info to welcome message
  • [x] Make loopfiles work in extensiondir
  • [x] Make renamemap work with workshop maps as well
  • [x] Subscribe maps and play subscribed maps
  • [x] Autocomplete maps (GUI)
  • [x] Download maps from servers and play from downloaded maps
  • [x] Render some kind of progress (use the passed ms maybe)
• [x] Authentication support
  • [x] Authenticate via Steam Ticket
  • [x] Allow for optional, required, disabled Steam auth mode
    • [x] Disconnect clients in required mode if no auth ticket can be found
  • [x] Bump protocol number
• [x] Other Steam features
  • [x] List servers with game mode, name, players, map, mode
  • [x] Connect to server when you click on a friends game