More efficient single account retrieval (0.9ms vs 50ms before)

db/migrate/20170322021028_add_lowercase_index_to_accounts.rb

@@ -0,0 +1,9 @@
+class AddLowercaseIndexToAccounts < ActiveRecord::Migration[5.0]
+  def up
+    execute 'CREATE INDEX index_accounts_on_username_and_domain_lower ON accounts (lower(username), lower(domain))'
+  end
+
+  def down
+    remove_index :accounts, name: 'index_accounts_on_username_and_domain_lower'
+  end
+end