Handling of booleans in CSV import

It is hard and not intuitive to use boolean attributes in CSV import.

Actual behavior

Setting TRUE in fixed values or CSV data does not work, you have to put 1. (this was tested on force GID, should be tested on other boolean fields as well to check consistency)

Expected behavior

• Boolean attributes should show TRUE and FALSE options as does SelectAttributes, without the need to add fixed values by hand
• When using fixed values or CSV data, TRUE and FALSE string should be supported since this is the LDAP representation for booleans. 0/1 should also work. (for booleans which use another LDAP representation, it should also support their LDAP representation - unless it’s reversed true/false)

This changes may impact webservices as well (csv import uses serialization on templates which I think webservice also use, should be checked)