FIX: whisper no longer experimental

- Regular users are not notified of whispers
- Regular users no longer have "stuck" topics in unread
- Additional tracking for staff highest post number
- Remove a bunch of unused columns in topics table

db/migrate/20161202011139_add_whisper_support_to_topics.rb

@@ -0,0 +1,16 @@
+class AddWhisperSupportToTopics < ActiveRecord::Migration
+  def up
+    remove_column :topics, :bookmark_count
+    remove_column :topics, :off_topic_count
+    remove_column :topics, :illegal_count
+    remove_column :topics, :inappropriate_count
+    remove_column :topics, :notify_user_count
+
+    add_column :topics, :highest_staff_post_number, :int, default: 0, null: false
+    execute "UPDATE topics SET highest_staff_post_number = highest_post_number"
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end