DevicePixelRatio or Other method to set scaling manually

[llelectronics]

I noticed on devices with smaller screens just like the Jolla the devicePixelRatio defaults to 1.0 which makes the fonts and overall webpages super small barely readable. The sailfish-browser uses devicePixelRatio 1.5.
There is no option to set the devicePixelRatio in QML.
I wrote a little patch to make it possible and called the thing deviceScaleFactor (actually it is in the cpp part but not exposed to qml)

It would fix this problem also reported here: https://together.jolla.com/question/1271/webview-scale-is-too-small/
and allows more flexibility when it comes to mobile apps.

Patch:
https://paste.kde.org/pjejyakjj

Feel free to improve it if necessary :)