Event Validation does not Throw Error

Created by: hermannsblum

Steps to reproduce:

Create an event with catchphrase_de, time_advertising_start and time_advertising_end. The API creates the event and sends 201 without any validation errors.

e.g. the following event was just created on the dev api: https://api-dev.amiv.ethz.ch/events/5c76eefbaa9d350001a3285b