Add ability to add a moderator by token

Modifies the Route PUT /room/{id}/moderator/{modId} with a RequestParam called token, to provide adding moderators by it´s own with this token.
The Route POST /room/{id}/moderator/{modId}/token is also added to generate a token for the user with the ID "modId" and the room with the id "id". This routes returns just the token as string (which can be used for example in a link for the frontend)