mobile app - wallet with NFC function for sending/receiving contact information and requesting DOI's

As another step to develop seamlessness of exchanging contact information and requesting contact permission, a NFC variant is planed. (also see: https://github.com/Doichain/dapp/issues/48)

This variant should work as the QR-Code variant but should also include a background service (Android and if possible on iOS) so another device (Bob) can send (and also receive) its contact information when touching the device of "Alice". A contact permission is requested afterwards to the corresponding dApp/publicKey.

So far the functionality possibilities of NFC on Android and iOS are not clear and need to be evaluated.