feat: openrefine icon compliant with new MacOS guidelines

[teolemon]

Fixes #6399

What

• feat: openrefine icon compliant with new MacOS guidelines

[tfmorris]

Thanks!

Pinging @OpenRefine/designers to see if they have any feedback.

[wetneb]

When pinging designers it's generally helpful to provide a screenshot for them to be able to judge the changes easily - especially since GitHub doesn't provide previews for .icns files. Here is one:

(the logo on the left-hand side is the new one, the old one is on the right-hand side)

[thadguidry]

still think we can go just a bit larger... to the maximum that's allowed for the icon grid? as I mentioned in this comment #6399 (comment)
Also add a drop shadow as I mentioned.
@wetneb I mean, look how our OpenRefine logo inside the white box compares to your Keys app as an example.

[wetneb]

@thadguidry I don't think we can go much larger because we are limited on the width by the white frame.

I'd merge this soon unless @teolemon wants to do further tweaks.