Add view for info / sign-up desks

[MarkusH]

During the conference a set of users need a permission to see some data of a user:

• Ticket is (not) paid (+ possibility to toggle state)
• Has bought a SIM card (+ possibility to toggle reception)
• Contact information
• Which, when and where talks / trainings are given
• Trainings attending
• If being a sponsor and which
• ... something more

Lookup should be possible by:

• User ID (part of the link to the porfile)
• Username
• E-mail-addres
• Name (full_name, display_name)
• Ticket ID
• Purchase ID
• Invoice number

[DasIch]

The idea here is to add a view (reachable via Admin menu) for search/lookup, which gives you a list of results which link to a view that shows the per-user detail. Search should be available from any of these locations.