Initial commit.

Adding focus on slider handle when video ends.
Removing unnecessary debug console.log() calls.
Change back to original code.
Adding comments.
Also undid tabindex=-1 for the slider knob. It is unnecessary, and prevents
the user from tabbing onto the slider.
Adding minor details.
startTime and endTime proper reset.

BLD-488
Adding tests.

Disabled Jasmine test due to flakiness on dev machine.
Added test for endTime in update().
Enabled updatePlayTime() tests. Will see on Jenkins.
Adding test for updatePlayTime() method.
Adding ProgressSlider notifyThroughHandleEnd() Jasmine tests.
Fixing Jasmine coverage problems.
Removed cover logs.
Fixing flaky test.
Removed code coverage logs.

BLD-488
Addressing reviewer's comments.

Updated Change Log.

BLD-488
Merge pull request #1677 from edx/valera/alert_screenreader_video_end

a11y - Videos need to alert screenreaders when the video is over.