Use Indico registration for "Bring your own script..." workshop (see #109)

This is a preparation in case today's discussion to self-host Indico ends in an "not feasible" verdict.

However, since some data needs to be collected from participants here, email registration is definitely not feasible here, thus this suggestion to use a cloned version of I cloned the event from https://schedule.tii.tu-dresden.de/event/20/.