Submission/unipro web animations 05

Tests for AnimationTimeline,play() method
testcommon.js file contains common routine for all web-animations tests. This PR contains only AnimationTimeline.play() tests but testcommon.js contains routine for other tests as well. So this variable is not used in tests from this PR but used in other tests. In particular, assert_approx_equals() and EPSILON used in AnimationPlayer tests (for testing current time for example)