Improvements for multi track feature

Created by: KozhinM

The PR adds two improvements for multiple adaptations feature: 1. Support of two more Specific Descriptors - Accessibility and AudioChannelConfiguration. They also can be used to set the initial audio/video settings along with Viewpoint, Role and lang. 2. Smarter logic to select the initial adaptation. Instead of picking the first one, there are two modes - select the track with the highest bitrate (default mode), or the track with a widest range of bitrates (number of representations in the adaptation set).

The improvements were proposed by @LloydW93 (thanks a lot!)