Implement the identity and all the process around to create a member identity

• Display a summary of what have to be done
• license approval
• define id, credentials with strong rules:
  • duniterpy#150 (closed)
  • mnemotic: PyPI, Debian
  • special char, lengh, use a python module for checking this rules
  • pip, haven’t found any package on Debian, YnH class.
• (warn that the credentials can’t be changed afterwards)? no longer true with v2 ecosystem
• save revocation document
• send the identity document
• propose to send the membership document