[Untested] Frontend user roles

Roles per user:

* [x] can have multiple
* [x] can always be team member
* [x] cant be scrum masters && product owner

Roles per project:

* [x] Cant have multiple product owners
* [x] Cant have multiple scrum masters

Test

* [ ] Test

Backend doesnt respond when sending requests:
```json
{
  "roles": ["Developer"],
  "user": 1,
  "project": 1
}
```