qmljseditor: do not complete private properties

Private properties (starting with __) are not offered as completion
unless one has already typed __*

Change-log: [Qml/JS Support] Do not show properties starting with "__" in auto-completion.

Change-Id: Iecf4c2ee5c14f12a45a26479328862d6a50b3ffb
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

src/plugins/qmljseditor/qmljscompletionassist.h

@@ -69,6 +69,7 @@ public:
         : TextEditor::BasicProposalItemListModel(items)
     {}
 
+    virtual void filter(const QString &prefix);
     virtual void sort();
     virtual bool keepPerfectMatch(TextEditor::AssistReason reason) const;
 };