MT#5629 Fix setting external_id in customer ctx.
MT#5661 Update prepaid pref on bilprof change

If prepaid flag is changed in billing profile, all subscribers
of all contracts currently having this profile are updated.

If customer changes from prepaid profile to postpaid and vice versa,
all subscribers of this contract are updated.

If subscriber is created either in subscriber or customer view,
the prepaid pref is set if billing profile of its customer is
prepaid.
MT#5661 change selection of customers when bprof is updated

only those customers which have this billing profile
currently active are considered
this concerns the change of the prepaid flag