Merge branch 'time-dependence' into 'collab_front'

backend/db/crud.py

backend/db/models.py

backend/db/schemas.py

backend/routers/stats.py

frontend/src/components/Graph.js

frontend/src/components/WaitingTime.js

frontend/src/components/index.js

frontend/src/index.js

frontend/src/views/Restaurant.js