With a mature history setting up a browser window can be slow, but
if it's setup at creation time it is extremely fast.
The signal prototype of MidoriBrowser::new-window had to change,
all call sites were adjusted.
We strip HTML from "title" elements when required now. And we
always try to show at least the URI for feeds in the WebKit view.
And we fallback to using the URI in the treeview if the title/
description is empty.
