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/qmljshoverhandler.h

@@ -80,7 +80,7 @@ private:
                       QmlJS::AST::UiImport *node);
 
     void prettyPrintTooltip(const QmlJS::Interpreter::Value *value,
-                            const QmlJS::Interpreter::Context *context);
+                            const QmlJS::Interpreter::ContextPtr &context);
 
     TextEditor::HelpItem qmlHelpItem(const QmlJS::LookupContext::Ptr &lookupContext,
                                      QmlJS::AST::Node *node) const;