Add option to change default settings

[CWempe]

If I host my own server I would like to change some default settings.

Like:

• default word set (e.g. German (Original))
• Fullscreen: ON/OFF
• Dark mode: ON/OFF (or AUTO)
• Timer ON/OFF
• basically every setting 😉

For docker this should be done by setting an environment variable.

Like:

docker run \
  --name codenames_server \
  --rm -p 9091:9091 \
  --env DEFAULTWORDSET="german_original" \
  --env FULLSCREEN="ON \
  -d codenames