Split out handy-user. Gather LookUp into one source file.  Add convenience methods to DAO

handy-user now contains the small User, Identity, and PasswordLogin classes

LookUp, LookUpOne, and LookUpMany have been moved into LookUp.scala

DAO has had versions of findMany, findOne, and findSorted that take Ref[BSONDocument] added.  These help shorten the code of DAO methods that take a Ref[T] rather than a RefWithId[T], as you can write
findMany(
  for { id <- r.refId } yield BSONDocument(...)
)