Implement an option for Staff Badge Printing stations to add an attendee manually

[mariobehling]

There should be two options for checking in attendees a) full self-checkin, b) assisted checkin by an organiser.

The assisted checkin enables an organiser to find attendees by name of email. They will have the option to checkin the attendee manually and print the badge.

This already worked on version 1 of the app.