Allow special characters for tax codes.

The following special characters are now permitted for tax codes:

'$'
'"'
'§'
'&'
')'
'/'
'='
'?'
'('
'#'

These tax codes are in the hex area between X'20' and X7F' and are therefore Unicode-compatible.

It is now possible to specify 46 *46 tax codes.

If you use the report RFBIBL00, you must not create any tax codes with the special character '/' because this is used as a "no data" indicator by the report RFBIBL00, which can lead to processing errors.
Alternatively, you can define a different "no data" indicator.