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/javascript/mastodon/features/status/components/detailed_status.js

@@ -213,7 +213,7 @@ export default class DetailedStatus extends ImmutablePureComponent {
             <DisplayName account={status.get('account')} localDomain={this.props.domain} />
           </a>
 
-          <StatusContent status={status} expanded={!status.get('hidden')} onExpandedToggle={this.handleExpandedToggle} />
+          <StatusContent status={status} expanded={status.get('activity_pub_type') === 'Article' || !status.get('hidden')} onExpandedToggle={this.handleExpandedToggle} />
 
           {media}