[sailfish-browser] Scale toolbar height and engine parameters by Theme.p...

...ixelRatio
I'm not sure if this actually should be just ```pixelRatio``` as it is exposed by WebUtils. Might be that ```cssPixelRatio``` is clearer.

In future we should refactor / rethink responsibilities of the WebUtils as well. Bad name and has extended its responsibilities over time. See also WebSettings. We could at least have have specific class for accessing gecko preferences, something like WebPreferences.