Add AS2 format to RABL files

app/views/accounts/show.activitystreams2.rabl

@@ -0,0 +1,8 @@
+extends 'activitypub/types/person.activitystreams2.rabl'
+
+object @account
+
+attributes display_name: :name, username: :preferredUsername, note: :summary
+
+node(:icon)   { |account| full_asset_url(account.avatar.url(:original)) }
+node(:image)  { |account| full_asset_url(account.header.url(:original)) }