Work on SegmentPullers/Loaders to make adding new SegmentPullers easier

There's more to do, I just wanted to make sure that it's the right direction before going forward. 

1) Move the local cacheFile logic out of the S3 pullers into the SingleSegmentLoader
2) Make the S3SegmentPuller just pull down the file
3) Make the Loader do the unzip, ungzip, or rename
4) 2 and 3 make S3ZippedSegmentPuller not necessary (still there, just deprecated and empty)
4) Tweak the TaskToolbox so that the Pullers returned by getSegmentGetters behave the same as they did before