Adding full Article support

This creates a new column in the `statuses` table which keeps track of
activity_pub_type, so in the case of a Note it will be blank (the
default) and it will be a string "Article" if the received remote object
is an AP Article. There is now a bunch of special case code in the
formatters and sanitizers to handle Articles differently, as well as on
the clientside.

app/lib/activitypub/activity/create.rb

@@ -60,7 +60,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
         account: @account,
         text: text_from_content || '',
         language: detected_language,
-        spoiler_text: converted_object_type? ? '' : (text_from_summary || ''),
+        spoiler_text: converted_object_type? ? '' : (text_from_summary || (@object['type'] == 'Article' && text_from_name) || ''),
         created_at: @object['published'],
         override_timestamps: @options[:override_timestamps],
         reply: @object['inReplyTo'].present?,
@@ -70,6 +70,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
         conversation: conversation_from_uri(@object['conversation']),
         media_attachment_ids: process_attachments.take(4).map(&:id),
         poll: process_poll,
+        activity_pub_type: @object['type']
       }
     end
   end