Allow the host to reject join requests

[kaenganxt]

Description

The host player should be able to prevent a player from joining the game.

Implementation hints

• (Optional) Add an option to the host game menu (Panels/HostGamePanel.cs) if joining players need to be accepted
• Create a new panel for asking the host if the player is allowed to join (see other panels in the Panels folder)
• Show the panel in Commands/Handler/Internal/ConnectionRequestHandler after the result command is sent.
• If the host rejects the request, disconnect the client
• If the host accepts, continue with the join process

[ghpdohmen]

I'm currently working on this. I'm struggling a bit with how to get the player name from the request handler to the panel in a clean way. Creating a PR for this