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:
    • For Debian.
    • For Ubuntu.
    • For Raspbian, although this platform is currently unmaintained (#74 (closed)).
    • For CentOS. This platform is currently unmaintained (#74 (closed)).
    • For FreeBSD. This platform is currently unmaintained (#74 (closed)).
    • For MacOS. This platform is currently unmaintained (#74 (closed)).
  • 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.
  • Create a configuration example.
  • Add into CI.
  • Test.
• Documentation:
  • Update the tutorial. Will leave that for the create command on #66 (closed).
  • Update the Using Onionspray page.
  • Update Mining Onion Service keys page.