Wizards should not re-use data that has entered before

Steps to reproduce (Example: Add Event):
1. Go to Recordings->Events
2. Press Add Event
3. Enter some metadata (e.g.) title and upload a file on the second page of the wizard without complete the add event wizard
4. Cancel the wizard
5. Press Add Event again

Actual Results:
The Add Event Wizard still has the data from the previous attempt of generating an event

Expected Results:
The Add Event Wizard should start from scratch, i.e. not remembering any data of previous event creations

Notes:
This even causes some serious mess, i.e. the add event wizard will upload wrong files in border cases