KIJIMR-80. Kiji MapReduce package reorganization.

 - Changes DistributedCacheJars audience to public.
 - Better JavaDoc for KijiTransformJobBuilder.
 - Adds audience annotation of framework to HFileReducerMapReduceJobOutput and moves it.
 - KijiTransform tool becomes KijiLaunchMapReduce. Command is 'kiji mapreduce'.
 - Javadoc of class and description of tool improved for clarity.
 - Tests updated.

Signed-off-by: Lee Sheng <lsheng@wibidata.com>