[#923] OAuth consumer improvements, fixes, refactoring.

config/config.exs

lib/pleroma/web/auth/authenticator.ex

lib/pleroma/web/auth/ldap_authenticator.ex

lib/pleroma/web/auth/pleroma_authenticator.ex

lib/pleroma/web/oauth/oauth_controller.ex

lib/pleroma/web/router.ex

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

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

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

mix.lock