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  Ah, I see the full conversation here now -- my apologies. What was the decision on the mobile release front today? Also would we move towards the context.application dictionary, or did you want to leave as-is?
FYI: @shnayder  Thanks