Import group membership data

[kainhofer]

Currently, importing group membership is only possible with the "normal" user import. Problems are:

• Membership always starts with the current date
• Importing a specific membership start date is not possible
• Importing a specific membership end date (either past or future) is not possible

Changing membership dates is only possible after import by going to the profile of each user and adjusting each membership manually.

Consequently, for importing membership data from a previous system, going through the database is the only viable solution for now.