Submission/unipro web animations 05

Tests for AnimationTimeline,play() method
To test whether `timedItem` is directly associated with a player, in addition to the check:

    timedItem.player !== null

you must also test

    timedItem.player.source == timedItem

See: https://web-animations.github.io/web-animations-spec/bikeshed/Overview.html#directly-associated-with-a-player