- implement breakout-rooms
- integrated into the participants panel
- managed by moderators
- moderators can send participants to breakout-rooms
- participants can join breakout rooms by themselve
- participants can leave breakout rooms anytime

Co-authored-by: Robert Pintilii <robert.pin9@gmail.com>
Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

Contributing all buttons in one place goes against the designs that we
set out at the beginning of the project's rewrite and that multiple of
us have been following since then.

Move display of audio muted, video muted, and moderator icons,
which make up the elements of the small video toolbar, into React
Components.

We seemed to be using the names "film strip" and "filmstrip" (and,
consequently, their source code-conscious forms such as film-strip,
FilmStrip, etc.) In order to comply with our coding style which requires
a consistent one name for a given abstraction, choose one name and
rename the uses of the other name.

Wikipedia has a definition of a "filmstrip", I couldn't find a "film
strip". I guess our abstraction can be seen as what's described there.
When I google "film strip", I get results about "filmstrip" at the top.
That's why I chose "filmstrip".

Certain uses of "film strip" such as interfaceConfig.filmStripOnly and
in the external API I left untouched in an attempt to preserve
compatibility.

I wasn't sure whether CSS was tangled in compatibility so I made a
choice and renamed there was well.