GODT-22: Frontend-backend

- GODT-1246 Implement settings view.
- GODT-1257 GODT-1246: Account and Help view
- GODT-1298: Minimal working build (panics)
- GODT-1298: loading QML (needs Popup window)
- GODT-1298: WARN: Adding PopupWindow not possible!
    In therecipe qt the `quickwidgets` classes are within `quick` module, but
    forgot to add library and include paths into cgo flags. Therefore
    compilation fails and it would be hard to patch therecipe in order to
    fix it.

    I am not sure if rewrite PopupWindow into go would make any difference,
    therefore I decided to use normal QML Window without borders.
- GODT-1298: Rework status window, add backend props, slots and signals.
- GODT-1298: Users
- GODT-1298: Login
- GODT-1298: WIP Help and bug report
- GODT-1178: MacOS dock icon control
- GODT-1298: Help, bug report, update and events
- GODT-1298: Apple Mail config and Settings (without cache on disk)

internal/frontend/qml/Configuration.qml

@@ -0,0 +1,73 @@
+// Copyright (c) 2021 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// ProtonMail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+import QtQuick 2.13
+import QtQuick.Layouts 1.12
+import QtQuick.Controls 2.12
+import QtQuick.Controls.impl 2.12
+
+import Proton 4.0
+
+Rectangle {
+    id: root
+
+    property ColorScheme colorScheme
+    property string title
+    property string hostname
+    property string port
+    property string username
+    property string password
+    property string security
+
+    implicitWidth: 304
+    implicitHeight: content.height + 2*root._margin
+
+    color: root.colorScheme.background_norm
+    radius: 9
+
+    property int _margin: 24
+
+    ColumnLayout {
+        id: content
+        width: root.width - 2*root._margin
+        anchors{
+            top: root.top
+            left: root.left
+            leftMargin   : root._margin
+            rightMargin  : root._margin
+            topMargin    : root._margin
+            bottomMargin : root._margin
+        }
+
+        spacing: 12
+
+        Label {
+            colorScheme: root.colorScheme
+            text: root.title
+            type: Label.Body_semibold
+        }
+
+        Item{}
+
+        ConfigurationItem{ colorScheme: root.colorScheme; label: qsTr("Hostname") ; value: root.hostname }
+        ConfigurationItem{ colorScheme: root.colorScheme; label: qsTr("Port")     ; value: root.port     }
+        ConfigurationItem{ colorScheme: root.colorScheme; label: qsTr("Username") ; value: root.username }
+        ConfigurationItem{ colorScheme: root.colorScheme; label: qsTr("Password") ; value: root.password }
+        ConfigurationItem{ colorScheme: root.colorScheme; label: qsTr("Security") ; value: root.security }
+    }
+}
+