4K export preset to create video files for Apple devices

Fixes an issue in which Closed Caption files could be incorrectly labeled as SDH subtitles when creating an iTunes Store Package

Fixes an issue in which the Navigation window fails to display the source clip when the Preview Window is zoomed

Launch screen displays correctly on OS X El Capitan

Adds iPhone 6s, iPhone 6s Plus, iPad Pro, and Apple TV (4th generation) to the Apple Devices compatibility list