Inactivity timeout

[lmoureaux]

Is your feature request related to a problem? Please describe.
People forget the client open.

Describe the solution you'd like
Have the client disconnect automatically after some time of inactivity. This means not moving the map, opening a menu, etc. This could be a full automatic disconnect or an automatic switch to observer status. Either way new UI is needed to warn the player before it happens and inform them afterwards. This should also come with an offer to reconnect.

Describe alternatives you've considered
A server-side implementation would prevent some exploits but tracking activity is more difficult (the player might be observing an attack by their allies, without sending any packets).

Additional context
Related to the RTS discussions, as this would allow much better accounting of time spent online.

FCW has this (#346):