Add support HiDpi

[ronleb]

Hello,

Could you add support for HiDpi screens?

http://doc.qt.io/qt-5/highdpi.html

Setting the environment variable QT_AUTO_SCREEN_SCALE_FACTOR to 1 scales the app and the notification dialogs but it does not seem to take scaling setting into account and notification icon becomes blurry (icon is fine without scaling)

Setup: Fedora 27 with Gnome 3.26

Thanks

[julekgwa]

@xoonz I have enabled the HiDpi support, can you please update the app and try again.