Changed output format of anonymization mapping to csv

See merge request !1

from 'key previous identifier fullname'
to 'key;previous identifier;fullname'

* Also the command line options should now work as expected
* Added an identity converter that just outputs .json output.
  This allows to postprocess files that have already been created.
* Breaking changes to the data format: students is now a list
* Bump python version to 3.5 to support typing