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/Proton/Button.qml

@@ -246,9 +246,25 @@ T.Button {
             }
         }
 
-        border.color: control.colorScheme.border_norm
+        border.color: {
+            return control.colorScheme.border_norm
+        }
         border.width: secondary && !borderless ? 1 : 0
 
         opacity: control.enabled || control.loading ? 1.0 : 0.5
     }
+
+
+    Component.onCompleted: {
+        if (!control.colorScheme) {
+            console.trace()
+            var next = root
+            for (var i = 0; i<1000; i++) {
+                console.log(i, next, "colorscheme", next.colorScheme)
+                next = next.parent
+                if (!next) break
+            }
+            console.error("ColorScheme not defined")
+        }
+    }
 }