Add support for authoringInformation sub-element to AudioProgramme.

[rsjbailey]

2076-2 adds a new optional sub-element authoringInformation to audioProgramme

authoringInformation has two sub-elements

referenceLayout

The reference layout describes the loudspeaker layout for which the content of the audioProgramme was originally produced for. In that sense it represents the optimal loudspeaker layouts from the content creator's point of view
It contains an audioPackFormatIDRef subelement

renderer

The renderer sub-element contains uri, name and version attributes to describe the renderer used in production and monitoring
It also has one or more audioPackFormatIDRef to describe the monitoring setups used during production