Fixes BatchedStore interval calculation

There was a bug in refactoring and interval calculation in BatchedStore. This fixes it and simplifies the interval calculation. Also fixes the Scalding unit tests to use batch cover in input space instead of store space. Fixes #567
do we need this? Can't we just read from the firstDeltaTimstamp, to timeSpan.upper? I don't see why we need the batching except to avoid doing the interval math. But that would just be a method like:

```def setLower(lb: InclusiveLower[Timestamp], interv: Interval[Timestamp]): Interval[Timestamp] = interv match {
  case u@Upper(_) => lb && u
  case Intersection(_, u) => lb && u
  case Empty() => Empty()
  case _ => lb // Otherwise the upperbound is infinity.
}