QmlJSEditorPlugin: Refactor

This follows the recently introduced pattern for plugin setup
- Pimpl QmlJSEditorPlugin
- remove unneeded uses of global object pool
- apply "static pattern"
- simplify some constructors of data members in some cases
- use in-class initialization in some case

Change-Id: I95b42d0885f4a8d6c9bfe1e4c004d3ace0a3eba5
Reviewed-by: Marco Benelli <marco.benelli@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/qmljseditor/quicktoolbar.cpp

@@ -74,12 +74,8 @@ static inline const ObjectValue * getPropertyChangesTarget(Node *node, const Sco
     return 0;
 }
 
-QuickToolBar::QuickToolBar(QObject *parent)
-    : ::IContextPane(parent)
-    , m_editorWidget(0)
-    , m_blockWriting(false)
+QuickToolBar::QuickToolBar()
 {
-    m_node = 0;
     contextWidget();
 
     m_propertyOrder