add an example that runs wordcount over file datasets

simple example to read and write files. 
- a service that can upload/download files
- a mapreduce that reads/writes the same files, with runtime arguments to specify the paths

I am open to renaming this, if you have a better suggestion. 
A service to upload or download files to the..
or
A service to upload files to the \"lines\" file Dataset or download files from the \"counts\" file Dataset.