BLD-1230: Video Link Obfuscation

A contextual menu has been added to non-YouTube videos.

**Ticket: [BLD-1230](https://openedx.atlassian.net/browse/BLD-1230)**

**Acceptance criteria:**
When a student right-clicks on a video, they are not presented with any of the following options:
 * Save video as
 * Copy Video URL
 * Copy Video Address
 * Open video in New Tab
 * Open Video in New Window
 * Save Snapshot As….
 * Email Video
 * Copy Video Location
 * View Video
 * Download Video
 * Download Video As

When a student right-clicks on a non-YouTube video, they are instead presented with options for controlling the video including:
 * Play (Pause)
 * Mute (Unmute)
 * Fill browser (Exit full browser) --> Only in LMS not Studio.
 * Speed (with a sub-menu populated with the default speed options of the browser i.e. 0.75x, 1.0x, 1.25x, 1.50x)

**Sandbox: studio.jmclaus.m.sandbox.edx.org**
[Direct link to example] (http://studio.jmclaus.m.sandbox.edx.org/container/i4x://edX/BLD1230/vertical/a5b2494e91584fabb43223cb0ec6ec62)

Or use the following mp4 [video] (http://vjs.zencdn.net/v/oceans.mp4) to test the contextual menu in your own course.

**@Lyla-Fischer @explorerleslie** Please review.
@cahrens 
> It's great that you have a test for this, but it doesn't work for me (in Studio). I wonder if it is
> because Fullscreen is not shown, and that is screwing up the keyboard navigation.

and

>I do believe it is related to Fullscreen being hidden, because the LMS works OK for me.
>Up and down doesn't work properly for keyboard navigation between the menu items (Play and >Mute) and the submenu item (Speed). One direction works, but the other does not.

You are right, it was the because Fullscreen was being hidden. The focus would land on it  and get stuck. It's fixed.