QmlDesigner.PropertyEditor: Checked is only valid if checkable is true

If checkable is false we disable the checked property CheckBox.

Change-Id: I128d78e15d0d711f33b4af191a4c24869ca37127
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>

src/plugins/qmldesigner/componentsplugin/Controls/ButtonSpecifics.qml

@@ -64,6 +64,7 @@ Column {
 
             SecondColumnLayout {
                 CheckBox {
+                    enabled: backendValues.checkable.value
                     text: backendValues.checked.valueToString
                     backendValue: backendValues.checked
                     implicitWidth: 180
@@ -82,6 +83,13 @@ Column {
                 CheckBox {
                     text: backendValues.checkable.valueToString
                     backendValue: backendValues.checkable
+                    property bool backEndValueValue: backendValues.checkable.value
+                    onTextChanged: {
+                        if (!backendValues.checkable.value) {
+                            backendValues.checked.resetValue()
+                        }
+                    }
+
                     implicitWidth: 180
                 }
                 ExpandingSpacer {