Updates videoSrc and videoCaptions props to accept <source>/<track> elements instead of arrays of
config objects. Also makes various improvements to the component's implementation which should help
it work more consistently.

BREAKING CHANGE: videoSrc prop only accepts an src URL string or a set of <source> elements instead
of arrays of config objects now, and videoCaptions prop only accepts <track> elements instead of
arrays of config objects

…e robust