Theming app and ImageMagick #7100

From #6460 (comment):

@skjnldsv You need imagemagick enabled in your webserver setup. Then the endpoint http://localhost/index.php/apps/theming/favicon/core should return an ico file with different sizes.

Is it possible to show a little indicator in the theming settings that show if imagemagick is properly running or not. Just a little hint with a checkmark "all is properly set up" or a little x or warning sign and "Enable/install the imagemagick PHP extension to automatically generate favicons based on the uploaded logo and color". Like we do in the admin settings.

cc @skjnldsv @juliushaertl