New section for video events emitted by mobile app, fixes DOC-1219

@nasthagiri , @stroilova , please verify the accuracy of all changed lines, particularly the new section for mobile video events and the existing section for browser video events.
@mulby FYI
@catong , @mhoeber , and @srpearce , events are expected to be in packages on Thursday. 
@nasthagiri - gotcha. I wasn't sure what state things were in. I kept seeing "app_name" but my later comment `I would really prefer the dictionary, is there a reason this can't be done? It turns out it is very hard to iterate on stuff like this since once we publish events with data in one location it is very cumbersome and time consuming to move it...` wasn't responded to so I was holding out hope that you started with the trivial fix, but you were going to try to fit in the preferred solution. I guess I didn't realize you had abandoned all hope of implementing the preferred solution.

I should have been more proactive about advocating for the first option and/or not even presented the other option if I wanted the first one so bad, sorry about that. Lets just move forward with it as is.