ActuatorSlider: hide (blue) indicator bar while not active

Particularly useful for servos, so it's clear which ones are controlled.

src/AutoPilotPlugins/PX4/ActuatorSlider.qml

@@ -44,6 +44,7 @@ Column {
         updateValueWhileDragging:   true
         anchors.horizontalCenter:   parent.horizontalCenter
         height:                     ScreenTools.defaultFontPixelHeight * _sliderHeight
+        indicatorBarVisible:        sendTimer.running
 
         onValueChanged: {
             if (blockUpdates)

src/QmlControls/QGCSlider.qml

@@ -22,6 +22,7 @@ Slider {
     // Value indicator starts display from zero instead of min value
     property bool zeroCentered: false
     property bool displayValue: false
+    property bool indicatorBarVisible: true
 
     style: SliderStyle {
         groove: Item {
@@ -40,6 +41,7 @@ Slider {
             Item {
                 id:     indicatorBar
                 clip:   true
+                visible: indicatorBarVisible
                 x:      _root.zeroCentered ? zeroCenteredIndicatorStart : 0
                 width:  _root.zeroCentered ? centerIndicatorWidth : styleData.handlePosition
                 height: parent.height