Show pages headers to go back to pane when needed

src/gui/Base/HPageHeader.qml

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+import QtQuick 2.12
+import QtQuick.Layouts 1.12
+
+Rectangle {
+    width: page.width
+    height: show ? theme.baseElementsHeight : 0
+    visible: height > 0
+    color: theme.controls.header.background
+
+
+    property HPage page: parent
+    property bool show: mainUI.mainPane.collapse
+
+
+    Behavior on height { HNumberAnimation {} }
+
+    HRowLayout {
+        anchors.fill: parent
+
+        HButton {
+            id: goToMainPaneButton
+            padded: false
+            backgroundColor: "transparent"
+            icon.name: "go-back-to-main-pane"
+            toolTip.text: qsTr("Go back to main pane")
+
+            onClicked: mainUI.mainPane.toggleFocus()
+
+            Layout.preferredWidth: theme.baseElementsHeight
+            Layout.fillHeight: true
+        }
+
+        HLabel {
+            text: page.title
+            elide: Text.ElideRight
+            horizontalAlignment: Qt.AlignHCenter
+            verticalAlignment: Qt.AlignVCenter
+
+            Layout.fillWidth: true
+            Layout.fillHeight: true
+        }
+
+        Item {
+            Layout.preferredWidth: goToMainPaneButton.width
+            Layout.fillHeight: true
+        }
+    }
+}