[#923] OAuth: prototype of sign in / sign up with Twitter.

config/config.exs

lib/pleroma/user.ex

lib/pleroma/web/auth/authenticator.ex

lib/pleroma/web/auth/pleroma_authenticator.ex

lib/pleroma/web/endpoint.ex

lib/pleroma/web/oauth/oauth_controller.ex

lib/pleroma/web/oauth/oauth_view.ex

lib/pleroma/web/templates/o_auth/o_auth/consumer.html.eex

lib/pleroma/web/templates/o_auth/o_auth/show.html.eex

...1315_add_auth_provider_and_auth_provider_uid_to_users.exs