Screen Sharing with Google Docs

As a GT user working with my team, I want to be able to share my screen so that my peers can look at what I'm sharing and see it clearly.

Acceptance Criteria

[x] Re-enable screen sharing in GT-Riff.
[x] When a user shares their screen, close any open Google docs that other participants have open so that the screen share can use that real estate.
[x] When documents close, tile the videos vertically, so that the sharing user can see the other people in the meeting while they share.

---- After Dev Review ---- As a user, I would like to be able to toggle btwn the shared screen of a presenter, so that I can take notes on what's being shared. Desired behavior:

[x] On screen share (all users including presenter) - minimize Doc if open, display shared screen in doc space, vertically tile participants to the left, make the far left video video of self - even for the presenter; allow all users to toggle the doc on and off, which will replace the shared screen in the main portion of the page. Once sharing is stopped, all users' main panel should revert to it the open doc (which is much easier technically than reverting to previous state).

Other items

[ ] Doc Icon looks like chat - use icons in the comments of story #220 instead.
[x] Riff chat shows in full screen view but does not work, don't display in that view.
[x] Audio doubled on screen share.
[x] Doc hide and expand adds a new anonymous user - possible to change via iframe open/close instead?

rifflearning / zenhub

Screen Sharing with Google Docs #235