[FIX] confirm lines of account cash statement on closing

The account_bank_statement_extensions adds a state field to account.bank.statement.line and sets the status to 'confirm' when a bank statement is closed. When a cash statement is closed, the lines remain in draft.

Steps to reproduce:
1. Install account_bank_statement_extensions
2. Open a cash register.
3. Add a cash transaction.
4. Close the cash register.

Observed behavior:
  The account.bank.statement.line corresponding to the cash transaction remains in status draft.

Expected behavior:
  The state of the line should be changed to 'confirm' as is the case in normal bank statements.