Fix server info
Due to the new connection handling, Gajim cannot display TLS version and used cipher anymore. This adapts the ServerInfo dialog. This enables Gajim to show if Direct TLS, Start TLS, or PLAIN is used. The connection's protocol (WebSocket/TCP) will also be displayed.
Additionally, this adds Esc as a hotkey to close the CertificateDialog.
Used proxy is commented out, as it will be added later.