Improve first-run UX

- Replace LoginPage with step-by-step approach to support different login flows
- Implement login using SSO

imports/NeoChat/Component/Login/Sso.qml

@@ -0,0 +1,42 @@
+
+/**
+ * SPDX-FileCopyrightText: 2020 Tobias Fella <fella@posteo.de>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+import QtQuick 2.15
+import QtQuick.Controls 2.12 as QQC2
+import QtQuick.Layouts 1.12
+
+import org.kde.neochat 1.0
+
+import NeoChat.Component 1.0
+
+import org.kde.kirigami 2.12 as Kirigami
+
+LoginStep {
+    id: root
+
+    title: i18nc("@title", "Login")
+    message: i18n("Login with single sign-on")
+
+    Kirigami.FormLayout {
+        Connections {
+            target: LoginHelper
+            onSsoUrlChanged: {
+                Qt.openUrlExternally(LoginHelper.ssoUrl)
+            }
+            onConnected: proccessed("qrc:/imports/NeoChat/Component/Login/Loading.qml")
+        }
+
+        QQC2.Button {
+            text: i18n("Login")
+            onClicked: {
+                LoginHelper.loginWithSso()
+                root.showMessage(i18n("Complete the authentification steps in your browser"))
+            }
+            Component.onCompleted: forceActiveFocus()
+            Keys.onReturnPressed: clicked()
+        }
+    }
+}