Add "logout" action to disconnect/error notifications

When a user disconnects or receives an error within a Guacamole connection, the dialog displays simply "Home" or "Reconnect". This is useful but particularly confusing in the case that a user has only one connection, as they will not have a home screen and the mechanism for logging out may not be apparent.

There should additionally be a "Logout" action presented at the end of a connection, both for convenience and easing confusion.