Support playing an annotation target

[benwbrum]

Annotations presented externally to the AVComponent may wish to use the component to play the targets of their annotations. The basic functionality missing from the current codebase is the ability to advance the player to a particular timestamp (outside of the private method _setCurrentTime on CanvasInstance, but several progressive enhancements might facilitate annotation targets:

Lower-level enhancement suggestions

• Adding an optional timestamp argument to play().
• Allowing CanvasInstance.setCanvas to accept a #t= fragment on the URI argument, parsing it to advance the player to the appropriate point.

Mid-level enhancement suggestions

• Supporting an end time as well as a start-time in the above, so that the player plays only the segment specified.

Higher-level enhancement suggestions:

• Accepting a JSON block corresponding to the target element of a WebAnnotation (including point selectors and range selectors as in this recipe and playing (or advancing) only that portion of the media.
• Accepting a (pair of?) URIs for an Annotation (and its containing AnnotationPage?) to be fetched by the component, parsed, and played as above.

This is intended as a starting point for discussion. Example use cases to follow soon.

[benwbrum]

For an example of similar functionality accomplished much less elegantly, see the links between annotation rows and the player here