More proeminent reminder for feedbacks

[fcamblor]

We could imagine a highly visible (almost annoying) in-app reminder that would only be displayed when the user has not given any feedback on timeslots where they have placed at least 1 favourite.

This could easily replace the + fab with a more proeminent message

We might mention in this disclaimer that there is only xxx hours left to give feedback (see #107)

[fcamblor]

@robinlopez made this ergonomic study:
https://github.com/user-attachments/assets/a026207f-a11f-453f-b985-7fee5c44bf14

The popup might be shown once for all (per event), when feedback buttons start to appear on some favourited talks (first time slots of the day, taking into consideration that there are some conferences, like devoxx, where people might not attend first days of the conference and should then not be bugged by the popup)

Reminder on the "plus" button on the bottom might expand regularly (every 4h if user clicks on "don't bother me for 4h") in order to regularly reminder/annoy the user about the fact that he needs to provide some feedback to speakers