Add full timestamps to all tables

Its convention to include these on all tables, so its really confusing
when they don't exist.

Initially we're setting them to allow `NULL` values so that we can write
and run a data population task without the records being invalid. We'll
then fixup these with a `null: false` constraint.

db/migrate/20180418154555_add_timestamps_to_foi_attachments.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToFoiAttachments < ActiveRecord::Migration
+  def change
+    add_timestamps(:foi_attachments)
+  end
+end

db/migrate/20180418154949_add_timestamps_to_holidays.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToHolidays < ActiveRecord::Migration
+  def change
+    add_timestamps(:holidays)
+  end
+end

db/migrate/20180418155130_add_updated_at_to_info_request_events.rb

@@ -0,0 +1,10 @@
+# -*- encoding : utf-8 -*-
+class AddUpdatedAtToInfoRequestEvents < ActiveRecord::Migration
+  def up
+    add_column :info_request_events, :updated_at, :datetime
+  end
+
+  def down
+    remove_column :info_request_events, :updated_at
+  end
+end

db/migrate/20180418155632_add_timestamps_to_profile_photos.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToProfilePhotos < ActiveRecord::Migration
+  def change
+    add_timestamps(:profile_photos)
+  end
+end

db/migrate/20180418155850_add_timestamps_to_public_body_category_links.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToPublicBodyCategoryLinks < ActiveRecord::Migration
+  def change
+    add_timestamps(:public_body_category_links)
+  end
+end

db/migrate/20180418155927_add_timestamps_to_public_body_categories.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToPublicBodyCategories < ActiveRecord::Migration
+  def change
+    add_timestamps(:public_body_categories)
+  end
+end

db/migrate/20180418160008_add_timestamps_to_public_body_headings.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToPublicBodyHeadings < ActiveRecord::Migration
+  def change
+    add_timestamps(:public_body_headings)
+  end
+end

db/migrate/20180418160048_add_timestamps_to_raw_emails.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToRawEmails < ActiveRecord::Migration
+  def change
+    add_timestamps(:raw_emails)
+  end
+end

db/migrate/20180418160204_add_timestamps_to_user_info_request_sent_alerts.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToUserInfoRequestSentAlerts < ActiveRecord::Migration
+  def change
+    add_timestamps(:user_info_request_sent_alerts)
+  end
+end

db/migrate/20180418160205_add_updated_at_to_has_tag_string_tags.rb

@@ -0,0 +1,10 @@
+# -*- encoding : utf-8 -*-
+class AddUpdatedAtToHasTagStringTags < ActiveRecord::Migration
+  def up
+    add_column :has_tag_string_tags, :updated_at, :datetime
+  end
+
+  def down
+    remove_column :has_tag_string_tags, :updated_at
+  end
+end

db/migrate/20180418160206_add_timestamps_to_acts_as_xapian_jobs.rb

@@ -0,0 +1,6 @@
+# -*- encoding : utf-8 -*-
+class AddTimestampsToActsAsXapianJobs < ActiveRecord::Migration
+  def change
+    add_timestamps(:acts_as_xapian_jobs)
+  end
+end