Session Hijacking - Keep session alive on client disconnect

[alxbl]

Currently, if an intercepted client disconnects while their session is hijacked, PyRDP will ignore the request for disconnect until the RDP client times out, after which point both connections (client - pyrdp and pyrdp - server) are disconnected. Dropping the hijacked session in the process.

It would be nice and not too complicated to disconnect the client smoothly while keeping the hijacked session active.

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This would also require minor UI improvements to mark the state of the client (something simple like: idle, active, disconnected) In fact, this might be a whole other feature that ties in with #148 and gives a smoother experience to session hijacking.

[alxbl]

To add to my initial description, here is what this would involve at the minimum:

• [ ] (Maybe) Modify the AttackerMITM to expose a isHijacked property.
• [ ] Modify the handler for the disconnect packet (from client) to keep the server-side channel alive when attacker is in progress
• [ ] Ensure that the handler for server disconnection drops the server channel even if there is not matching client
• [ ] Modify the release control behavior so that if the client is gone, a disconnection sequence is sent to the server