macOS Big Sur App icon update.

[setanarut]

Closes #591

[sefsh]

I know that the party's over but since the merge is fairly new I just wanted to post an iteration of the decided one that I made:

It is still conforming to Big Sur guidelines but exhibits a bit more dynamism, imo.

[setanarut]

@yusf it is not compatible for white background color. discussed here #591 (comment) #591 (comment) Following the macos guidelines does not mean it is correct. I think a lot of Big Sur system icons are badly designed. especially those with white backgrounds and bad colors (safari, launchpad, photos, findmymac)

[sefsh]

Agreed it doesn’t sit well on white, though it’s just a draft and could well be improved upon. Besides, it’s made to look good in the dock and in the application switcher which both uses background blur making sure that the icon is never placed on a white background.