Restore the top-level function wrapper in the concatenated build files.

Switched to slightly different toolchain for building the concatenated
JS files. The earlier version has causesd some problems, because they
lost the top-level function wrapper they used to have.

The challenge here was to have source maps that point to the original
coffee files, and a concatenated JS file which contains all the code,
with a single top-level function wrapper. And a preamble.

The solution was to introduce (a fork of) [coffeebar](https://npmjs.org/package/coffeebarx),
which is capable of concatenating multiple source files, adding a top-level
wrapper, and generating source maps the point back to the original files.

This, together with mapcat and uglifyjs can do what we want.
Further build tweaks (mostly about source maps)

Now coffeebarx is used for building the annotator plugins JS files, too.
Also, all source files (belonging to the generated sourcemaps)
are copied to the same directory.

(It's easier to deploy the resulting bundle this way.)

The requirements have been updated, so don't forget to run `npm install`.
Fix sourcemap references at end of minified files

The newline was ending up in the source files as a literal "\n", rather
than as a newline.