Replace DenseRowTextStorage with raw mr job

@markhibberd I haven't done anything significant here (yet), expect for order the dictionary the way it was. I'm assuming there is more we want to do as well but you didn't get time. I'm happy to finish it up, and might look more closely at what you've done after lunch.

/cc @raronson 
It doesn't need to be deterministic across runs. It just needs to be consistent with the dictionary output for the run. Long term we can make it consistent if we want - but it is definitely not a requirement (and it will change when the dict changes anyway).