Add a new build-time dependency and update some existing ones.

Review Request #11000 — Created April 10, 2020 and submitted — Latest diff uploaded


This introduces a new dependency on babel-plugin-django-gettext, which
will allow us to have more clean localization in the JavaScript
codebase, taking advantage of multi-line strings and easy variable
references using template literals without worrying about the impact on
whitespace or the message scanner. This new plugin is also set up to be
activated in Babel.

It also updates some existing build-time dependencies, capping the
version ranges on a few and updating to the latest versions of
beanbag-docutils, kgb, and less.

Updated all dependencies, verifying that they installed correctly and had
the expected versions.

Built packages and ran unit tests successfully.