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 would be great to have all this non-Video code (up to the end, where the video context menu itself is defined) in a shared location. If this happens, this code should be unit-tested independently of the video usage.```

Yes, the goal for the long term is to unify the various menus in the video player. There is a significant amount of redundant code (and associated tests) in the following files:

```
035_video_accessible_menu.js
08_video_speed_control.js
095_video_context_menu.js
```
(```07_video_volume_control.js is a kind of its own```)

@polesye and I decided that it was not in the scope of this PR to refactor the above files. Our tentative plan is to make sure the contextual menu is stable and then proceed to further unification.