Added custom event triggered when a new multi value field is added after changing a certain field.
Added custom event triggered when a new multi value field is added after changing a certain field.

silverstripe-australia/silverstripe-multivaluefield,designcity/silverstripe-multivaluefield,silverstripe-australia/silverstripe-multivaluefield,designcity/silverstripe-multivaluefield,souldigital/silverstripe-multivaluefield,souldigital/silverstripe-multivaluefield