Allow multiple pinned statuses to be shown and make them be ordered b… (#4690)

* Allow multiple pinned statuses to be shown and make them be ordered by pinned date

* Set timestamps NOT NULL

* Make single-line pinned_statuses

* Spec for pinned_statuses

* Remove redundant empty line

app/models/status_pin.rb

@@ -6,6 +6,8 @@
 #  id         :integer          not null, primary key
 #  account_id :integer          not null
 #  status_id  :integer          not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
 #
 
 class StatusPin < ApplicationRecord