Basic qr parsing

Okay, so this is the long awaited feature to be able to support receiving QR codes from Qrca via commandline. (At least on XDG desktop based environments.)

I am not entirely happy about the (top-level) QML side of this. I don't like how I keep needing to add more and more bits of boolean state and then have to implement control flow derived from that. It feels like there ought to be a better way but that gets into architecture things that previously people felt too complex/overkill.

Suggestions welcome! Also, please test that this actually works on Plasma Mobile (kind of the point of the MR ;) )