Add export function

[Maismaus]

I used the generator but now I'd like to be able to export as image.

[Dennis-Rosenbaum]

That sounds like a good idea! Would you mind the image type? Like png, jpg, etc..

[Maismaus]

I'm not sure, for completeness sake both would probably make sense but png is probably best if you have to choose!
Also being able to specify the qr image dimensions would be nice.