account_bank_statement/account_voucher usability improvements

Usability improvements when using account_voucher in combination with bank_statement processing : - Generate & maintain accounting moves from within a bank statement on a line by line basis. - Replace the "F1/F2 create/open voucher" function keys by buttons. - Bank statement line buttons : the green arrow creates/opens Voucher or Move, the Delete button removes draft Vouchers or Moves. - For AR/AP general accounts the account_voucher object is used for reconciliation, for other accounts a regular move is created. - When no partner has been entered on the bank statement line a search view is presented to find and select matching AR/AP transactions without a partner filter. - An intermediate selection screen is presented in case of multiple outstanding invoices. This screen is pre-filled with the matching line(s). - The reconciled amount is shown on the bank statement line. An exclamation mark indicates differences between the paid amount and the open transactions. - The possibility to delete a Bank Statement with associated Posted Vouchers or Moves has been disabled. - Tax Codes and Tax Base Amounts can be added to the generated Accounting Moves in order to facilitate the encoding of bank costs. - The Bank Statement Confirm behaviour has been changed: at Confirm time a Posted Move will be created for Bank Statement Lines with no or Draft Moves. - Accounting Entry Changes are blocked for Moves linked to a Confirmed Bank Statement. - The creation of Payment Voucher on Confirmed Bank Statements is not allowed. - Otherwise 'orphaned' Voucher Lines are removed when the associated Accounting Entry Line is deleted. - Remove Vouchers created from an invoice (e.g. via invoice 'Payment' button) when the invoice is cancelled. - Remove Vouchers created from a bank statement line when the Voucher reference is removed from the bank statement line. - Generate Voucher number and Move name from bank statement number and line. - Update Partner records with Bank Account Number information during reconciliation (including BBAN->IBAN conversion).