Add rule to check the usage of apple-touch-icons

[alrra]

• Check if the <link> tag (e.g. <link rel="apple-touch-icon" href="apple-touch-icon.png">) is specified

  Note: In the past, people usually just had the apple-touch-icon in the root of the site, but that is no longer consider a good practice and can create a lot of issues (see: Rename Apple touch icon & add <link> in index.html h5bp/html5-boilerplate#1622).

• Check if a 180×180px image is not used

• Check if multiple multiple images of different sizes are used

  Note: Usually iOS devices get upgraded pretty quickly, most people being on the latest 2 version of the iOS, so specifying multiple sizes of the apple-touch-icon just adds to the weight of the page, without no real benefit. One 180×180px apple-touch-icon is nowadays enough for all cases, as Safari will scale it down automatically if needed (see also: Is there any need for the 6 different apple-touch icons when just one will work?  h5bp/html5-boilerplate#1367).

• Check if the image has transparent background

• Other?

[CKGrafico]

Sorry for the reference, different repo!