[16.0][FIX] web_calendar_slot_duration: fixing behavior on slot duration

[imlopes]

Convert all to float : if we use a context like {'calendar_slot_duration': '01:30:00'} we will have on the backend a duration of 10 hour and 30 minutes instead of 1 hour and 30 minutes

And using a slot_duration > 1 hour, the calendar view will be adapted to the slot duration but has not a good presentation. So I'm adding a possibility to adapt or not the calendar view using adapt_view_to_slot_duration on the context too.