Lobby - allow reconnect without returning to the main menu

[elexis]

If you are in the lobby and become disconnected, then in order to rejoin you have to return to the main menu and start the login process from scratch (Back -> Multiplayer -> Lobby -> Login -> Connect). The client doesn't attempt to reconnect by itself.

We could have a "Reconnect" button with the same size and position as the "Host" button that is only visible while we are disconnected. If clicked, it should attempt to rejoin without the need to provide the credentials again.

[elexis]

The new 'Connect' button would just have to do few calls that we find in lobbyStartConnect() of prelobby.js and reuse some code of init of lobby.js (could be moved to a new helper function) and call it from the "connected" case in lobby.js.