Convert external_acl_type directive format tokens

Convert external_acl_type directive format tokens

Use libformat tokenizer and string assembler mechanisms instead of
custom code for external helpers. This allows any logformat code and
transaction data to be used by the external ACL helper.

The old helper format tokens are added to the libformat for backward
compatibility.

Known issue:
  all access lists which use an exetrnal_acl_type helper now require
  setting up the ACL Checklist with an AccessLogEntry referencing any
  special token data the old format tokens needed.