Add support of synthetic navigation to HTTP driver

[ziflex]

Right now, pages created by in-memory http driver does not support navigation between pages due to their static nature.
It makes it problematic to "move" from one static page to another within a same domain simply because we cannot reuse current page. In order to do so, we have to create a new page every time we need to move from A to B.
Let's add a possibility to reuse existing page by implementing synthetic navigation that would just download a new HTML page by a given URL and replace root element.