Register/Login screens

[kova98]

Unauthorized users trying to create a review should be shown a register/login screen.

• [x] Backend (5c1470b858a3f5e74ecab584b287f62d25bc31c1)
• [x] Login screen (fc6e2e5dc13bfd31ccd74c33a77f7b3ff95cd94e)
• [x] Register screen (ce7bc6dc9aee52140b392f099847e348f596baf1)