Add xlsx export option to CSV output

[tballison]

As soon as anyone tries to open a csv with Unicode data in Excel, there will be problems. We should change the default output format for the csv writer to xlsx. We need to implement the xlsx writer, but there are examples in tika-eval.

We should leave in the option to write a true UTF-8 csv for those who want to do post-processing in python or something else that can actually read the files, unlike Excel.