refactor: Event management & colors

[gouz]

I refactor the events management. Instead of passing the event into each days, I create a global window object window.events structured like this:

{ year : { month : { day : [events] } } }

As example:

{ '2024' : { '1' : { '2' : [{event1}, {event2}] } } }

I add the navigation system too:

close #339
&
close #424

[scraly]

Suggestion: use the existing back and next buttons
Bug: the scrollTo feature is not working at the first click on a day

[scraly]

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