Add Clear All button

src/QmlControls/AppMessages.qml

@@ -43,8 +43,22 @@ QGCView {
                     id:         categoryColumn
                     spacing:    ScreenTools.defaultFontPixelHeight / 2
 
+                    QGCButton {
+                        text: qsTr("Clear All")
+                        onClicked: {
+                            var logCats = QGroundControl.loggingCategories()
+                            for (var i=0; i<logCats.length; i++) {
+                                QGroundControl.setCategoryLoggingOn(logCats[i], false)
+                            }
+                            QGroundControl.updateLoggingFilterRules()
+                            categoryRepeater.model = undefined
+                            categoryRepeater.model = QGroundControl.loggingCategories()
+                        }
+                    }
+
                     Repeater {
-                        model:      QGroundControl.loggingCategories()
+                        id:     categoryRepeater
+                        model:  QGroundControl.loggingCategories()
 
                         QGCCheckBox {
                             text:       modelData