REFACTOR: Replace score bonuses with low/med/high priorities

We removed score from the UX so it makes more sense to have sites set
priorities instead of score bonuses.

db/migrate/20190522194332_add_priority_to_post_action_types.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class AddPriorityToPostActionTypes < ActiveRecord::Migration[5.2]
+  def up
+    add_column :post_action_types, :reviewable_priority, :integer, default: 0, null: false
+    execute(<<~SQL)
+      UPDATE post_action_types
+      SET reviewable_priority = CASE
+        WHEN score_bonus > 5 THEN 10
+        WHEN score_bonus > 0 THEN 5
+        ELSE 0
+      END
+    SQL
+  end
+
+  def down
+    remove_column :post_action_types, :reviewable_priority
+  end
+end