improve support for MPEG_media properties (autoplay, loop)

[nlsdvl]

Currently autoplay and loop properties of media are not honoured, this is blocking the implementation of media support interractity scenes.

These are the properties currently parsed but not honoured by the player:

• autoplay
• loop
• startTimeOffset
• endTimeOffset
• autoplayGroup
• controls (per. media instance controls: texture, audio sources)

The above list is ordered by priority (tbd).