Integrate auction

Closes #874

db/migrate/20181212105100_create_auctions.rb

@@ -0,0 +1,27 @@
+class CreateAuctions < ActiveRecord::Migration
+  def up
+    execute <<-SQL
+      CREATE TYPE auction_status AS ENUM (
+        'open',
+        'closed_without_winner',
+        'closed_with_winner',
+        'payment_received'
+      );
+    SQL
+
+    create_table :auctions do |t|
+      t.string :domain, null: false
+      t.column :status, :auction_status, null: false
+      t.uuid :uuid, default: 'gen_random_uuid()', null: false
+      t.datetime :created_at, null: false
+    end
+  end
+
+  def down
+    execute <<-SQL
+      DROP type auction_status;
+    SQL
+
+    drop_table :auctions
+  end
+end