MT#4955 Only allow one ss, set dom-pref np-display

If a sound set is contract default and you create another default one,
the old gets non-default.

Properly handle contract default setting also when editing sound sets.

And while at it, set np-display as outbound-from-display-name dom-pref
when creating a PBX domain.
MT#5009 Properly re-use free numbers.

Don't try to insert a number into billing.voip_numbers directly,
rather than using the update_subscriber_numbers helper, which
handles the re-using of free numbers.
MT#5009 Properly free voip_numbers on termination.

Don't delete voip_numbers (which was forgotten if the status
got set to terminated anyways), rather than free them by
undef'ing the subscriber_id and reseller_id.
Bump debian version to 1.1.4 for 3.1 release.