Mandatory Cash manager (Kasverantwoordelijke) selection upon creating an event.

Ghost User
2017-12-10T21:19:02+01:00

When creating an event, the user must select whether a money-box is needed. If so, he must select the cash manager for the event.
### Desired behaviour
For administration purposes, the board should be notified when a money-box is needed for an event at least a week in advance.
When an event is created, one should select whether a money-box is needed. If so, he must select a user which will then be cash manager for this event. Upon creation, the selected cash manager is notified by email. The board is notified once per week, also by email, containing all new events that require a money-box.