Added script to convert repository.csv to a xlsx file.

With https://github.com/4teamwork/opengever.core/pull/254 the import of the repository changed from `csv` to `xlsx`.

We converted all the excel files provided by our customers to `csv` to import them. We don't have all the excel files anymore, so all is left are the `csv` files. We now have to convert them back to a valid `xlsx` to make sure we can still setup the clients.

This script takes the valid header from `examplecontent.xlsx` and replaces the content with the data of a `repository.csv`

Original Issue: https://github.com/4teamwork/opengever.zug/issues/54

@lukasgraf @phgross