Keep gamesetup open after disconnect

[elexis]

When becoming disconnected while in gamesetup, it will close the page and return to the main menu or lobby. It would be preferable if the window could remain open, so that the chat sent just before the disconnect is still visible.

For example that helps in specifying kick/ban reasons, allows posting the reason why the host stopped the server or might show some tips on how to fix network issues.

Besides the return button, all buttons become disabled. The current (alpha 20 and previous) lobby implementation has this feature too. A "rejoin" button could be implemented for both cases, but might need some non-trivial rewriting (can be done in another ticket).