Replaced the favicon embedded in kiwix-serve with a slightly better one (taken from https://www.kiwix.org/favicon.ico).
Added favicon files for a number of devices. All files and html code is generated by: https://realfavicongenerator.net/ The file used to generate favicons can be found at: https://upload.wikimedia.org/wikipedia/commons/b/b0/Kiwix_logo_v3.svg
