Only build jscoq (+ addons) in Docker phase.

We reorganize jsCoq's source code as to be more modular, in particular
we start to place backend files under the `backend` directoy, and
frontend files under `frontend`.

Code as it now does work, note however that still quite a bit of work
is needed. In particular, the headless frontend should get its own
directory, the coq-jslib directory should go away, use more types,
etc...

Sync `package.json.wacoq` with `package.json`.

+ updated Mocha (npm audit stuff).

- Migrated patches for 8.14.
- Up wacoq to 8.14 in docker image
- install: 8.14 requires `coq-core` and `coq-stdlib` to be installed.
- Set version 0.14.0.

Quote escaping hell in this tiny `sed` script.

Previous package, `vue-context`, is abandoned.

So that we can create both jsCoq and waCoq packages.

Consolidated Webpack config in a single file, as is more common for
Webpack.
Provided npm scripts for running it as usual.

This was too hasty: vue-loader@16.x only works with Vue 3.

Some NPM audits.

Now `stream-browserify` is needed as a dependency.

This is phrased as an "addon"; I think that not only libraries can be
"addons" but this kind of interop UI functionality should be as well.

It does not mean that UI addons should be built outside of the jsCoq
source tree like mathcomp & co.
If they are small enough, they are ok where they are in `ui-js/addon`.

https://github.com/101arrowz/fflate/issues/17

Nothing too remarkable, code-wise, but a big change upstream is the
addition of `zarith` as a hard dependency.

TODO:

- update addons

Upgraded mocha and switched to async version of child_process.

What was needed in order to run unit tests in Node.js is
now located in `headless.ts`.
It is invoked via the regular CLI (bundled with Webpack).

Fixes #195.

This allows for the use of Vue's template compiler at build time,
reducing package footprint.

^^