GODT-1667: bridge-gui spawns bridge process. [skip-ci]

Other: renaming of bridge-gui.
WIP: locate bridge exe.
WIP: bridge process launch.
WIP: cleaner closure of bridge.
WIP: grpcClient connection retries.
WIP: clean exit when bridge process is killed.

Fixed issues from MR review. [skip-ci].

WIP: Fixed gRPC case in CMakelists.txt [skip-ci]

It caused issues on Debian.

WIP: update gRPC/protobuf and tweaked CMakeLists.txt. [skip-ci]

WIP: Fixed a bug where splash screen could not be dismissed. [skip-ci]

internal/frontend/bridge-gui/qml/Proton/Menu.qml

@@ -0,0 +1,72 @@
+// Copyright (c) 2022 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail 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.
+//
+// Proton Mail 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 Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+
+import QtQuick 2.12
+import QtQuick.Controls 2.12
+import QtQuick.Controls.impl 2.12
+import QtQuick.Templates 2.12 as T
+import QtQuick.Window 2.12
+import "."
+
+T.Menu {
+    id: control
+
+    property ColorScheme colorScheme
+
+    implicitWidth: Math.max(
+        implicitBackgroundWidth + leftInset + rightInset,
+        contentWidth + leftPadding + rightPadding
+    )
+    implicitHeight: Math.max(
+        implicitBackgroundHeight + topInset + bottomInset,
+        contentHeight + topPadding + bottomPadding
+    )
+
+    margins: 0
+    overlap: 1
+
+    delegate: MenuItem {
+        colorScheme: control.colorScheme
+    }
+
+    contentItem: Item {
+        implicitHeight: children[0].implicitHeight + children[0].anchors.topMargin + children[0].anchors.bottomMargin
+        implicitWidth: children[0].implicitWidth + children[0].anchors.leftMargin + children[0].anchors.rightMargin
+
+        ListView {
+            anchors.fill: parent
+            anchors.margins: 8
+
+            implicitHeight: contentHeight
+            model: control.contentModel
+            interactive: Window.window ? contentHeight > Window.window.height : false
+            clip: true
+            currentIndex: control.currentIndex
+
+            ScrollIndicator.vertical: ScrollIndicator {}
+        }
+    }
+
+    background: Rectangle {
+        implicitWidth: 200
+        implicitHeight: 40
+        color: colorScheme.background_norm
+        border.width: 1
+        border.color: colorScheme.border_weak
+        radius: Style.account_row_radius
+    }
+}