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.

app/views/api/activitypub/outbox/show_page.activitystreams2.rabl

@@ -0,0 +1,16 @@
+extends 'activitypub/types/ordered_collection_page.activitystreams2.rabl'
+
+object @account
+
+node(:items) do
+  @statuses.map { |status| api_activitypub_status_url(status) }
+end
+
+node(:next)       { @next_page_url } if @next_page_url
+node(:prev)       { @prev_page_url } if @prev_page_url
+node(:current)    { @first_page_url } if @first_page_url
+node(:first)      { @first_page_url } if @first_page_url
+node(:last)       { @last_page_url } if @last_page_url
+node(:partOf)     { @part_of_url } if @part_of_url
+
+node(:updated)    { |account| (@statuses.empty? ? account.created_at.to_time : @statuses.first.updated_at.to_time).xmlschema }