Add/set missing properties to/in DTOs

* Set the collaborator email in the GetCollaboratorDTO
objects returned by BucketsController#getCollaborators

* Set the defaultLayout property in GetBucketDTO
Fix NoResultException

* This exception is thrown when calling getSingleResult()
and no entry was found in the database. The fix is to use
getResultList() so that a null value is returned when the
return list is empty.
Jackson ObjectMapper: Ignore unknown properties