Turn NeoChatConnection::isVerifiedSession into a notifiable property

This should allow the devices page to hide the "Verify this Device"
warning, once you actually complete verification. I also made sure to
update the other consumer - the menu item under the user menu.

Additionally, I also fixed the password field not being automatically
focused when trying to remove a device.

src/app/qml/AccountMenu.qml

@@ -88,7 +88,7 @@ KirigamiComponents.ConvergentContextMenu {
     Kirigami.Action {
         text: i18nc("@action:inmenu", "Verify This Device")
         icon.name: "security-low"
-        visible: !root.connection.isVerifiedSession()
+        visible: !root.connection.isVerifiedSession
         onTriggered: {
             root.connection.startSelfVerification();
             const dialog = Qt.createComponent("org.kde.kirigami", "PromptDialog").createObject(QQC2.Overlay.overlay, {