Add network with QR scan

[Tbaut]

substrate networks are identified by genesisHash for Substrate.
We want to be able to add a new network (hence a new genesisHash) from a QR code scanned from a trusted source.

Upon scanning a "add new genesis hash" QR code:

• verify that the paypload has been signed by a Parity key
• the user should ideally not be asked for anything else than "be careful and double check everything".

Ideally we should put a color, name and prefix in the scanned data as well so that users don't need to choose or select anything on the signer.

cc @yjkimjunior and @maciejhirsz