Fix audio overlay showing up randomly.

Fixes #305

src/monitor/view/MonitorRuler.qml

@@ -8,6 +8,7 @@ import QtQuick 2.4
 Rectangle {
     id: ruler
     color: activePalette.window
+    property bool containsMouse: rulerMouseArea.containsMouse
 
     Timer {
         id: zoneToolTipTimer

src/monitor/view/kdenliveclipmonitor.qml

@@ -119,7 +119,7 @@ Item {
             QmlAudioThumb {
                 id: audioThumb
                 objectName: "audiothumb"
-                property bool stateVisible: true
+                property bool stateVisible: (barOverArea.mouseY >= root.height * 0.7 || dragOverArea.containsMouse || clipMonitorRuler.containsMouse)
                 anchors {
                     left: parent.left
                     bottom: parent.bottom
@@ -129,15 +129,6 @@ Item {
                 width: parent.width
                 visible: root.showAudiothumb
 
-                MouseArea {
-                    id: mouseOverArea
-                    hoverEnabled: true
-                    onExited: audioThumb.stateVisible = false
-                    onEntered: audioThumb.stateVisible = true
-                    acceptedButtons: Qt.NoButton
-                    anchors.fill: parent
-                }
-
                 states: [
                     State { when: audioThumb.stateVisible;
                         PropertyChanges {   target: audioThumb; opacity: 1.0    } },