Clarify documentation for QML object ownership

The documentation for the QQmlEngine::ObjectOwnership enum (http://qt-project.org/doc/qt-5.1/qtqml/qqmlengine.html#ObjectOwnership-enum) states in two different areas:

• "When the object is returned to QML as the return value of a method call or property access, QML will track it, and delete the object if there are no remaining JavaScript references to it..."

• "...objects returned from C++ method calls; in these cases, the ownership of the returned objects will be set to JavaScriptOwnerShip. Note this applies only to explicit invocations of Q_INVOKABLE methods or slots, and not to property getter invocations."

The information for objects accessed via property isn't clear (are they given Cpp or JavaScript ownership?).