Add. Handle `b` legs in CDR. (#2626)

* Add. Handle `b` legs in CDR.

CDR list/statistic by default handle only `a` legs.
So it prevent display wrong result when b-leg turn on.
Add ability to write to db `b` legs only for specific call directions.

To be able see b-legs in CDR need set xml_cdr_b_leg permission.
To add specific call direction to filter need add element to `cdr/b_leg/array` in default/domain settings.

* Add. `b_leg` to defalut settings.