Change ActivityPub paging to match spec. Clean up ActivityPub outbox changes. (#2410)

* Change ActivityPub paging to match spec. Clean up ActivityPub outbox changes.

* Fix code style and test failures for OutboxController.

* Attempt to fix CI errors.

config/application.rb

@@ -64,7 +64,7 @@ module Mastodon
     config.middleware.insert_before 0, Rack::Cors do
       allow do
         origins  '*'
-
+        resource '/@:username',  headers: :any, methods: [:get], credentials: false
         resource '/api/*',       headers: :any, methods: [:post, :put, :delete, :get, :patch, :options], credentials: false, expose: ['Link', 'X-RateLimit-Reset', 'X-RateLimit-Limit', 'X-RateLimit-Remaining', 'X-Request-Id']
         resource '/oauth/token', headers: :any, methods: [:post], credentials: false
       end