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/qt/log/log.go

@@ -0,0 +1,46 @@
+// 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/>.
+
+// +build build_qt
+
+// Package log redirects QML logs to logrus
+package log
+
+//#include "log.h"
+import "C"
+
+import (
+	"github.com/sirupsen/logrus"
+	"github.com/therecipe/qt/core"
+)
+
+var logQML = logrus.WithField("pkg", "frontent/qml")
+
+// InstallMessageHandler is registering logQML as logger for QML calls.
+func InstallMessageHandler() {
+	C.InstallMessageHandler()
+}
+
+//export logMsgPacked
+func logMsgPacked(data *C.char, len C.int) {
+	logQML.Warn(C.GoStringN(data, len))
+}
+
+// logDummy is here to trigger qtmoc to create cgo instructions
+type logDummy struct {
+	core.QObject
+}