- Expose an api on Filmstrip to hide the remote videos container, which does so
  by adding a class
- Modify listeners for user join, leave, share video to call the api
- Hide the container when there is 1 or fewer remote participants
- Always show the container if self view is in focus
- Show the container if the number of remote thumbnails does not match the count
  of remote participants, such as the case of sharing a video

The 1:1 call UI and vertical filmstrip act on remote videos
while leaving local video alone. To facilitate acting only on
remote videos, place remote videos into their own container element.

All z-indexes found in css files have been moved into css
variables. If the z-index is used only once, the variable
name will be the same as the selector it is used in. If
the z-index is used multiple times, then the plain name
of $zindex# was used. This allowed a more confident
moving down of the toolbar so that the new modal dialog,
with z-index 500, could display on top of it.

#1436