Name: multi-registration
Type: request
Purpose: >
  Instruct the server to create multiple participant objects
Response: multi-registration-confirmation
Inherits: message
Elements:
  Event-Id: { type: identifier, class: event }
  Count: { type: integer, min_value: 1, max_value: 10000 }
Notes:
  The Count element tells the server how many participant objects
  have to be created.
Rejection-Codes:
  22: Invalid value for count
  23: Estimated turnout does not allow that much participants
  31: Sender is not authorized to register participants
  41: Event does not exist