The Omni Group has released a major update to its flagship OmniFocus productivity application for iPhone and iPod touch users. OmniFocus 1.7 adds new refreshed high-resolution artwork for the iPhone 4 Retina display and adds support for several of the multitasking features introduced in iOS 4. When running on the iPhone 4, iPhone 3GS and third-generation iPod touch, OmniFocus 1.7 now provides fast app switching, local notifications of due tasks and…