Rename Apple touch icon & add <link> to index.html

Ref https://github.com/h5bp/html5boilerplate.com/commit/71b10e177111b0835000b2113359008702aefb79
    https://github.com/h5bp/html5-boilerplate/issues/1615
    https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html