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/tests/ButtonsColumn.qml

@@ -0,0 +1,76 @@
+// 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.Layouts 1.12
+import QtQuick 2.12
+import QtQuick.Controls 2.12
+
+import "../Proton"
+
+ColumnLayout {
+    id: root
+    property ColorScheme colorScheme
+
+    property string textNormal: "Button"
+    property string iconNormal: ""
+    property string textDisabled: "Disabled"
+    property string iconDisabled: ""
+    property string textLoading: "Loading"
+    property string iconLoading: ""
+    property bool secondary: false
+
+    Button {
+        colorScheme: root.colorScheme
+        Layout.fillWidth: true
+
+        Layout.minimumHeight: implicitHeight
+        Layout.minimumWidth: implicitWidth
+
+        text: root.textNormal
+        icon.source: iconNormal
+        secondary: root.secondary
+    }
+
+
+    Button {
+        colorScheme: root.colorScheme
+        Layout.fillWidth: true
+
+        Layout.minimumHeight: implicitHeight
+        Layout.minimumWidth: implicitWidth
+
+        text: root.textDisabled
+        icon.source: iconDisabled
+        secondary: root.secondary
+
+        enabled: false
+    }
+
+    Button {
+        colorScheme: root.colorScheme
+        Layout.fillWidth: true
+
+        Layout.minimumHeight: implicitHeight
+        Layout.minimumWidth: implicitWidth
+
+        text: root.textLoading
+        icon.source: iconLoading
+        secondary: root.secondary
+
+        loading: true
+    }
+}