Sign in flow without Account on Gnokey

[iuricmp]

Implement the use case where dSocial redirects to Gnokey mobile but there is no account on Gnokey mobile.
Gnokey mobile must display a message encouraging the user to create an account.

Expected scenario:

1. User opens dSocial (or any 3rd party app), presses sign in button
2. dSocial redirects to Gnokey mobile app.
3. On Gnokey mobile the user can select the account
4. Gnokey mobile redirects back to dSocial passing the account address as a parameter
5. User is signed in dSocial