Added price currency to conference, select currency in basic info and created data rake task for setting old conferences' price currency

db/migrate/20190713163405_add_price_currency_to_conferences.rb

@@ -0,0 +1,5 @@
+class AddPriceCurrencyToConferences < ActiveRecord::Migration[5.1]
+  def change
+    add_column :conferences, :price_currency, :string, default: "USD"
+  end
+end