Allow return to lobby from ESC menu

[heaventwig]

Currently, ESC by default in most screens brings up a dialogue window with two choices: quit or don't quit.

If this enhancement were added, there would be a third option, return to lobby. Selecting that option would bring the client back to the SNIS lobby screen, where it's possible to select a server (list shows each as a set of {IP, instance, protocol, location, connections} and has a cancel button to return to the network setup screen).

[smcameron]

Returning to the lobby is not so easy, because when you connect to snis_server the connection to the lobby server is closed. But for a start, we can allow disconnecting from snis_server, which will take you back to the network setup screen.

• 1c4748f Add disconnect button to quit screen