[Enhancement] Add script icon to userscript header

[ae5960e8-a6fc-491f-b252-898ecf59af95]

The line below can be added to the // ==UserScript== area so the logo of the script shows up in our script manages. I suggest using the logo for the project here.

Example from another project:
// @ICON https://raw.githubusercontent.com/DenverCoder1/Unedit-for-Reddit/3.9.4/images/logo128.png

As you can see, many other scrips take advantage of this feature, and it would make a good addition.

[victornpb]

I have no idea why I haven't added this yet 😂, I thought I've done it but I realized I didn't.
Thank you for reminding me of that.

[victornpb]

Implemented on 5.1 #456