Add option to create foodcoop transaction when creating a collection

This option can be used, if a kind of "double-entry accounting" is used
and every transaction should have a corresponding transaction.

app/views/finance/financial_transactions/new_collection.html.haml

@@ -68,6 +68,11 @@
   %p
     = link_to t('.new_ordergroup'), '#', 'data-add-transaction' => true, class: 'btn'
     = link_to t('.add_all_ordergroups'), '#', 'data-add-all-ordergroups' => true, class: 'btn'
+  - if FinancialTransaction.where(ordergroup: nil).any?
+    %p
+      %label
+        = check_box_tag :create_foodcoop_transaction, true, params[:create_foodcoop_transaction]
+        = t('.create_foodcoop_transaction')
   - if BankAccount.any?
     %p
       %label