Valera/video alpha2 refactor

This is the Video Alpha version 2. A refactored version of the Video Alpha which is currently in master. Several key differences:

1.) Controls are auto hidden after a delay of mouse inactivity - the full video becomes visible.
2.) When captions (CC) button is pressed, captions stick (not auto hidden after a delay of mouse inactivity). The video player size does not change - the video is down-sized and placed in the middle of the black area.
3.) All source code of Video Alpha 2 is written in JavaScript. It is not a basic conversion from CoffeeScript. The structure of the player has been changed.

It is fully backward compatible with the original Video Alpha XModule, and with the Video XModule. It is a drop-in replacement.

The Jasmine JavaScript tests have been rewritten and updated. There are 9 test files and they all pass.

PS: When you are running the tests in chrome locally, make sure that chrome is started with the option "--allow-file-access-from-files".

PPS: Don't forget to place test video files (test.mp4, test.ogv, test.webm) into the folder "common/lib/xmodule". You can get these from http://www.quirksmode.org/html5/tests/video.html or from some other site that demonstrates HTML5 video playback. Just open up the site's source, and save the video files (make sure to rename them to "test.*").

This information is included in the file common/lib/xmodule/xmodule/js/spec/videoalpha/readme.md file.

@rocha and @peter-fogg please review!