QmlJS: Share Context.

Previously Context was not entirely thread safe and had to be
copied locally. Now it is thread safe and its lifetime
managed by QSharedPointer.

The non-safe parts were moved into ScopeChain in a previous commit.

Change-Id: I851a93de85cbd6391dbea0fe33b011e2e093addb
Reviewed-on: http://codereview.qt.nokia.com/1695
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>

src/plugins/qmljseditor/qmloutlinemodel.cpp

@@ -99,7 +99,7 @@ void QmlOutlineItem::setItemData(const QMap<int, QVariant> &roles)
     }
 }
 
-QString QmlOutlineItem::prettyPrint(const Interpreter::Value *value, const Interpreter::Context *context) const
+QString QmlOutlineItem::prettyPrint(const Interpreter::Value *value, const Interpreter::ContextPtr &context) const
 {
     if (! value)
         return QString();