Added environment variables for ports, game mode, and server takeover

[mcronce]

Also shrunk the image a little and fully-qualified some paths :)

[dwurf]

Thanks! A nice set of fixes :)

Couple of issues:

• Can you please document the new variables?
• KF_WEBADMIN_PORT=7777 -> should be KF_WEBADMIN_PORT=8080

I will try the changes out on my server later, hopefully tonight.