Monitor effect toolbar: center to prevent covering top/bottom handles.

Fixes #1044

src/monitor/view/EffectToolBar.qml

@@ -22,6 +22,7 @@ MouseArea {
         objectName: "effecttoolbar"
         width: fullscreenButton.width
         anchors.right: barZone.right
+        anchors.verticalCenter: parent.verticalCenter
         height: childrenRect.height
         color: Qt.rgba(activePalette.window.r, activePalette.window.g, activePalette.window.b, 0.7)
         opacity: 0

src/monitor/view/kdenlivemonitorcornerscene.qml

@@ -228,7 +228,7 @@ Item {
         anchors {
             right: parent.right
             top: parent.top
-            topMargin: 4
+            bottom: parent.bottom
             rightMargin: 4
             leftMargin: 4
         }

src/monitor/view/kdenlivemonitoreffectscene.qml

@@ -611,7 +611,7 @@ Item {
         anchors {
             right: parent.right
             top: parent.top
-            topMargin: 4
+            bottom: parent.bottom
             rightMargin: 4
             leftMargin: 4
         }

src/monitor/view/kdenlivemonitorrotoscene.qml

@@ -719,7 +719,7 @@ Item {
         anchors {
             right: parent.right
             top: parent.top
-            topMargin: 4
+            bottom: parent.bottom
             rightMargin: 4
             leftMargin: 4
         }