Facebook&rsquo;s iPhone app has been a perennial favorite on Apple&rsquo;s handset, so it&rsquo;s always been a bit of a mystery as to why the social network didn&rsquo;t have an app designed for the iPad. Last year, Facebook founder and CEO Mark Zuckerberg said it was because &ldquo;the iPad&rsquo;s not mobile . . . it&rsquo;s a [...]