Use summarizers to make compaction decisions

[keith-turner]

In Accumulo 2.0 summarizes were introduced. Fluo could use these to count column types and notifications. These counts could be use to make compaction decisions.

[keith-turner]

It would be better to do this after Accumulo 2.1.0 releases w/ new compaction updates. Doing it now would require writing code against the Accumulo CompactionStrategy which is deprecated as of Accumulo 2.1.0 because its highly unstable.