Used icons on roomielib.com

Icons are from https://game-icons.net and are used under CC BY 3.0:
https://creativecommons.org/licenses/by/3.0/

Local copies are stored in `html/assets/icons/game-icons/`.
The website inlines these icons directly in `html/index.html`.

- doorway by Lorc
  https://game-icons.net/1x1/lorc/doorway.html
- circuitry by Lorc
  https://game-icons.net/1x1/lorc/circuitry.html
- three-friends by Delapouite
  https://game-icons.net/1x1/delapouite/three-friends.html
- broken-wall by Delapouite
  https://game-icons.net/1x1/delapouite/broken-wall.html
- convince by Delapouite
  https://game-icons.net/1x1/delapouite/convince.html
- gate by Delapouite
  https://game-icons.net/1x1/delapouite/gate.html
- house by Delapouite
  https://game-icons.net/1x1/delapouite/house.html
- console-controller by Skoll
  https://game-icons.net/1x1/skoll/console-controller.html
- power-generator by Delapouite
  https://game-icons.net/1x1/delapouite/power-generator.html
- door-ring-handle by Delapouite
  https://game-icons.net/1x1/delapouite/door-ring-handle.html
- locked-door by Delapouite
  https://game-icons.net/1x1/delapouite/locked-door.html
- team-idea by Delapouite
  https://game-icons.net/1x1/delapouite/team-idea.html