Enable user to scan settings with QR code

[cribskip]

As discussed in #708, we should enable the user to scan settings by QR code - speeding up setup and reducing errors.

This should be enabled in https://github.com/openhab/openhab-cloud and https://github.com/openhab/openhab.ios to keep a consistent UX.

Suggested Workflow:

1. User registers with openhab-cloud
2. Creates his/her users
3. QR code is shown, openhab-apps offers scan
4. Code is scanned, Data is parsed and saved in settings

[JohannesPtaszyk]

What excactly is meant by data?
Server, Username and Password?
I would like to implement that feature, but I am not really into web programming, so it would be nice to have someone who would help me with the webend.

[mueller-ma]

I'm going to close this issue since it needs some server-side work before implemented in the client.