have user register email through rpc

[gnunicorn]

[gnunicorn]

it is now possible to define custom rpc functions. we need to upgrade our polkadot api then we can define and use the existing "register_email" functions - polkadot-js/api#1504

[gnunicorn]

functions are there, need to be added to frontend, but on the official one we are currently not sending emails. Now that #24 is fixed, we might want to look into changing that though...