Reintrdocuce tenant column

Until we merge the feature that always turns on tenancy
(mbulat#79), we must keep
the dummy Rails app's migrations disjoint from what
`rake plutus:migrations:install` actually copies over

fixture_rails_root/db/migrate/20180709082453_tenant_plutus_tables.rb

@@ -0,0 +1,6 @@
+class TenantPlutusTables < ActiveRecord::Migration[4.2]
+  def change
+    # add a tenant column to plutus accounts table.
+    add_column :plutus_accounts, :tenant_id, :integer, index: true
+  end
+end

fixture_rails_root/db/schema.rb

@@ -10,14 +10,15 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170710173916) do
+ActiveRecord::Schema.define(version: 20180709082453) do
 
   create_table "plutus_accounts", force: :cascade do |t|
     t.string "name"
     t.string "type"
     t.boolean "contra"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.integer "tenant_id"
     t.index ["name", "type"], name: "index_plutus_accounts_on_name_and_type"
   end