QmlJSEditor: Add completion for JS keywords and Qml reserved words.

Task-number: QTCREATORBUG-919
Reviewed-by: Roberto Raggi

src/libs/qmljs/qmljsscanner.h

@@ -87,6 +87,7 @@ public:
     int state() const;
 
     bool isKeyword(const QString &text) const;
+    static QStringList keywords();
 
 private:
     int _state;