[#468] Prototype of OAuth2 scopes support. TwitterAPI scope restrictions.

lib/pleroma/plugs/oauth_scopes_plug.ex

lib/pleroma/web/oauth.ex

lib/pleroma/web/oauth/authorization.ex

lib/pleroma/web/oauth/oauth_controller.ex

lib/pleroma/web/oauth/token.ex

lib/pleroma/web/router.ex

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

...igrations/20190208131753_add_scope_to_o_auth_entities.exs

...s/20190209123318_data_migration_populate_o_auth_scope.exs