Allow plugins to receive the data context of DOM areas

[oliverfoster]

adapt-graphicLottie and adapt-graphicVideo allow any graphics to be replaced with svg animations and videos. They do this by listening for dom changes where img tags are injected, specifically img tags with bespoke file extensions, and the extensions replace those img tags with a relevant player. Sometimes it is necessary to configure those players locally on the _graphic object, such as for instance specific looping and controls.

It would therefore be nice to know to which _graphic object the img tag belongs in the course data.