Adding new Compaction Strategy

- Based off LeveledCompaction, but allows for levels to be overlapping
  at a level higher than 0
- When an overlapping compaction has occurred, and no other compactions
  are necessary, OCS will work on de-overlapping the levels
- A new tool has been added to nodetool, 'getmanifest', which allows for
  the inspection of where in the levels the SSTables currently are