Show scrollbars for a few seconds at first

Lets the user know that there's content to scroll.

src/gui/Base/HFlickable.qml

@@ -11,6 +11,7 @@ Flickable {
     ScrollBar.vertical: HScrollBar {
         visible: parent.interactive
         z: 999
+        flickableMoving: flickable.moving
     }
 
     Component.onCompleted: {

src/gui/Base/HGridView.qml

@@ -84,6 +84,7 @@ GridView {
 
     ScrollBar.vertical: HScrollBar {
         visible: gridView.interactive
+        flickableMoving: gridView.moving
     }
 
     // property bool debug: false

src/gui/Base/HListView.qml

@@ -100,6 +100,7 @@ ListView {
     }
 
     ScrollBar.vertical: HScrollBar {
+        flickableMoving: listView.moving
         visible: listView.interactive
     }
 

src/gui/Base/HScrollBar.qml

@@ -6,6 +6,8 @@ import QtQuick.Controls 2.12
 ScrollBar {
     id: scrollBar
 
+    property bool flickableMoving
+
     minimumSize: (Math.min(height / 1.5, 48) * theme.uiScale) / height
     opacity: size < 1 && (active || hovered) ? 1 : 0
     padding: 0
@@ -34,5 +36,18 @@ ScrollBar {
         }
     }
 
-    Behavior on opacity { HNumberAnimation {} }
+    onFlickableMovingChanged: if (flickableMoving) activeOverride.when = false
+
+    Behavior on opacity { HNumberAnimation { factor: 2 } }
+
+    Binding on active {
+        id: activeOverride
+        value: initialVisibilityTimer.running
+    }
+
+    Timer {
+        id: initialVisibilityTimer
+        interval: window.settings.autoHideScrollBarsAfterMsec
+        running: scrollBar.size < 1
+    }
 }

src/gui/Base/HScrollView.qml

@@ -11,6 +11,5 @@ ScrollView {
         x: scrollView.mirrored ? 0 : scrollView.width - width
         y: scrollView.topPadding
         height: scrollView.availableHeight
-        active: scrollView.ScrollBar.horizontal.active
     }
 }