Icon galleries updates

With Apple's new branding around their operating systems, I brought the icon galleries representations into a more unified whole:

Apple Watch icon gallery (applewatchicongallery.com) is now watchOS icon gallery (watchosicongallery.com)

iOS icon gallery (iosicongallery.com) stays the same.

Mac icon gallery (macicongallery.com) is now macOS icon gallery (macosicongallery.com)

And tvOS icon gallery is coming soon...