User should not be able to enable demo mode if there already is an access
STR:
- On a fresh new Kresus (no access), open two tabs, on onboarding
- On the first tab, create a bank access
- On the second tab (not synced with the first), enable the demo mode
What happens:
Kresus now has both the demo access + the previous access. Which is not an issue yet, but when the demo mode is disabled, all the accesses will be deleted.
What is expected:
The server should send back an error when enabling the demo mode if there already exist bank accesses.