Make it possible to set token on participant creation in authenticated audience (3)

When a participant is created from the web interface in an authenticated audience, it is not possible to set the token. This is only possible after the participant has been created. This is a little bit weird and the token should be added to the create participant modal to fix this.

We decided to implement this by adding a token field to the create participant modal. This field will have a randomize button next to the token field in the modal. This is the most flexible solution. It is clear to the organizer what to do, and even if the organizer did at first choose a deterministic token, he/she can still randomize it. This button could also be implemented in the edit modal for an anonymous audience and the edit modal for a participant.

To do:

• Create ES6 class that generates random tokens (1).
• Create React component that can put the generated random tokens into a form field (1).
• Add a field for having a token to the 'Add Participant' modal of an authenticated audience (1).
• Add the new React component for generating random tokens to the 'Edit Participant' modal of an authenticated audience (1).