Add QObject pointer to QQmlError for containing scope of errors

Exceptions in javascript bindings result in QQmlError objects sent via the QQmlEngine::warnings signal. They only include the line number where the error occurred and the text of the exception. They do not include the QObject where the error occurred. For example:

file:///automount/sun-01/home/mvisser/workspace/pug/imports/Pug/ShotgunDataFromElement.qml:9: TypeError: Cannot read property '-1' of undefined

I'd like to know which QObject triggered this exception.

I think this is a straightforward change:
1. add a QObject *object property to QQmlError (object/setObject) that defaults to 0
2. in QQmlJavaScriptException::exceptionToError call error.setObject(scopeObject())