Make possible to specify circle to use when doing QR code invitation

[goffi-contrib]

Creating a QR code directly from the app is really handy to easily invite somebody you see in person.

However, there is no way currently to specify in which circle the invited user must be added, resulting in the user being added to default circle, and see all contacts (which may not be desirable).

It would be really useful to be able to specify the circle to use when generating a QR code invitation.

Thanks.