Investigate adding ASYNC methods to Accumulo

In #593 async commit was added. The actual asynchronous writes to Accumulo were done in a hacky way that works, but is sub-optimal. The reason the current method is sub-optimal is that mutations and conditional mutations that are finished may not trigger follow on actions immediately until other unrelated data is processed. If the Accumulo itself supported async callbacks it could make the callbacks immediately when something finished processing.