Cleanup snapshot mr jobs

- Set BytesWritable capacity
- Do not recreate PrioritizedFactBytes
- Rename PrioritizedFactBytes to PriorityTag
- Change outputKey to BytesWritable mutating it for each key
You need this:
```scala
implicit def seqToResult[T](r: Seq[MatchResult[T]]): Result = 
  r.foldLeft(StandardResults.success: Result)(_ and _.toResult)
```