[ Feature Request ] Export/Import identy/s with qrcode

As the mobile version is spreading, I think that it can be good to have a more userfriendly way to import/export private key/s of the identies.

So, this is the request, I think that ZeroNet should show the qrcode of the private keys of the identies.

On this way the user from the mobile app, will be able to import the desktop identity/s by simply scanning it.

@canewsin Also this is required on the mobile app (currently missing), I mean, it should be easy to import/export them by simply scanning them.

No files, tests, or entry points are mentioned. Start by locating ZeroNet's identity private-key import/export flow and the mobile app's identity handling, then determine a QR representation that supports scanning between desktop and mobile. Done means identities can be exported and imported through QR codes without exposing incompatible or incomplete key data.

Written by the indexing model from the issue text.