This PR takes The Bulldozer Approach (R): removes the old toolbox and lots of
associated code, though not all of it. Subsequent cleanups will follow.

- Modify Etherpad and SharedVideo so their resizing takes into account
  the width of the filmstrip in vertical filmstrip mode.
- Modify Filmstrip's getFilmstripWidth to account for when the filmstrip
  is hidden.
- modify VideoContainer so in vertical filmstrip mode it centers the
  shared desktop stream in the middle of the available space not taken
  by filmstrip.
- Also allow clickthrough on the secondary toolbar itself while still
  allowing clicks on the toolbar's buttons. This allows clicks on
  shared videos to go through.

Prepares for the latest eslint & flow-related npm packages which cause
these errors.

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.

Enable ESLint on jitsi-meet with the same configuration and the same
goals as in lib-jitsi-meet.

This reverts commit 93648f361b.