better readable IBAN (#824)

display IBANs in groups of 4 digits with whitespaces in between

app/views/finance/bank_accounts/index.html.haml

@@ -11,6 +11,6 @@
     - for account in @bank_accounts
       %tr
         %td= link_to account.name, finance_bank_account_transactions_path(account)
-        %td= account.iban
+        %td= format_iban account.iban
         %td= truncate account.description, length: 50
         %td.numeric{style: 'width:5em'}= format_currency account.balance

app/views/finance/bank_transactions/show.html.haml

@@ -10,7 +10,7 @@
 - if @bank_transaction.iban?
   %p
     %b= heading_helper(BankTransaction, :iban) + ':'
-    = @bank_transaction.iban
+    = format_iban @bank_transaction.iban
     - if user = @bank_transaction.user
       = t('.belongs_to_user')
       = user.display

app/views/finance/invoices/unpaid.html.haml

@@ -23,7 +23,7 @@
     %p
       - if supplier.iban.present?
         %b= heading_helper(Supplier, :iban) + ':'
-        = supplier.iban
+        = format_iban supplier.iban
         %br/
       %b= t('.invoices_text') + ':'
       = invoices_text.join(', ')