Vanity address generation

Description

Onionspray could have a built-in mechanism for generating a Vanity Onion Service address.

Tasks

• Implementation:
  • Vendorize Onionmine.
  • Include Onionmine dependencies in Onionspray's installation procedure.
  • Implement the needed configuration options so Operators can specify that the .onion address for the service should match a given pattern.
  • Update the configuration step to run Onionmine if needed, in a way that only a single key is generated.
• Documentation:
  • Update Mining Onion Service keys pages.