Add option to create a financial_link when creating financial_transaction

If multiple financial transaction belong to a bank transaction, it
is sometimes easier to create them as a collection and add the bank
transaction instead of adding all financial transaction to a link
created via a bank transaction.

config/locales/en.yml

@@ -863,6 +863,7 @@ en:
         title: New transaction
       new_collection:
         add_all_ordergroups: Add all ordergroups
+        create_financial_link: Create a common financial link for the new transactions.
         new_ordergroup: Add new ordergroup
         save: Save transaction
         set_balance: Set the balance of the ordergroup to the entered amount.