invisible captcha + active hashcash = (#2744)

Gemfile

Gemfile.lock

app/assets/javascripts/devise.js

app/controllers/users/registrations_controller.rb

app/controllers/users/sessions_controller.rb

...models/communication/website/agenda/event/localization.rb

app/models/communication/website/page.rb

app/views/devise/registrations/new.html.erb

app/views/devise/sessions/new.html.erb

config/initializers/active_hashcash.rb

config/initializers/invisible_captcha.rb

...24215711_create_active_hashcash_stamps.active_hashcash.rb

db/schema.rb

test/controllers/users/registrations_controller_test.rb