Turns Response into a QObject and sets parent to the
command that emits it.
Each Command is also a child of the decorator commands,
Timeout and PageLoading commnds, so that deleting the
top level command will delete all the children.
See discussion in #430.
QWebFrame::url() does not return a valid URL for iframes. We can't just
look up the requested URL in m_responses because the request may have
been redirected, so instead we keep track of redirects and set up the
NetworkResponse when the final reply is received.
Matthew Horan