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. 
The point was that the mapreduce uses FileSet. I changed it to:
Application with a MapReduce that uses a FileSet dataset.