Mobile events, updates to video events

@stroilova , @mulby , @nasthagiri , @gwprice , @lou-wang , @mhoeber here is a framework that we can work from to get initial documentation out with the release. Notes:
- I am not sure that the same additional context fields that I see for the v.0 play_video (Olga shared with me) event also apply to all of the other video events.
- the event field names for the new edx.app.browser.launched event in Olga's spreadsheet are very rough
Yes. @lamagnifica , legacy video events have an 'id' in the browser and a 'module_id' field in the mobile app. The 'module_id' field is the full identifier of this video component.
Example:  "module_id": "i4x://MITx/4.605x_2/video/8b375e7e9c6d419c92a5cdc32f47d4f2"
More details in the main spec & wiki page.