Add visual indicators of event attendance

[toadjaune]

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Feature description

Hi folks,

When you get invited to an event, you can answer whether you'll be attending or not, and your participation to such an event has 4 possible states :

• Attending
• Not attending
• Tentative ("Maybe")
• Not specified (You have been invited but have not answered)

Currently, only the "Not attending" state is visually different from the rest (the event title is striked through)

I propose that we visually differenciate all of those 4 states from each other, possibly optionally if it's felt that this could be disliked / be a disruptive change.

There's a discussion to be had about the exact visual representation, but I personally like a lot the choice Google Calendar made, ie :

• Attending -> solid color background
• Not specified -> white background with color border and text
• Not attending -> white background with color border and text + strikethrough event title
• Tentative -> dashed color background

Why do you want this feature?

I personally like a lot to be able to tell whether I have already taken a decision about attending an event, and if so, which one, even from a very meta view of my calendar.

This is even more useful when the event creator relies on this mechanism to know who will attend ; in this case, not forgetting to answer is essential to the logistics. Adding a visual indicator ensures you won't forget, without having to actively check each event.

Additional information

If I understand well, for CalDav, attendance is manifested in the PARTSTAT parameter of the ATTENDEE property (see RFC 5545 #3.8.4.1)