#11884 - New child windows now inherit the settings of the parent

I hope I did this right. My C++ is rather rusty, and I'm just now familiarizing myself with phantom's code.

This fixes(I hope properly) part of issue #11884, in which child pages created from links, window.opens, etc in an initial page, do not inherit the parent's settings, such as the user agent.

However, it does not provide means of changing a child window's settings separately, before the child page is loaded. I'm guessing a new hook might be needed for that?