It’s been a big week for YouTube news. On Wednesday, the company launched a new HTML5-based mobile site, as well as the slick-looking YouTube Leanback. Today, during a keynote at VidCon, the site made a few more announcements: YouTube is adding support for video shot in the 4K video format — a very high resolution that clocks in at 4096 x 3072). And it’s also creating a new $5 million Partner Grants program that’s meant to help spur the...