* Streamlines devcontainer Dockerfile and adds fontconfig

fontconfig enables running pulse rendering tests in a devcontainer
with a headless JVM. The Dockerfile has been streamlined and a comment
added to explain the additional requirement.

* Adds rlwrap (for clj command)

https://nodejs.org/en/download/package-manager/#debian-and-ubuntu-based-linux-distributions

* To be able to run a devcontainer its own network (not just --net
host), webpack-dev-server serves on 0.0.0.0.
* Fix expired signature (EXPKEYSIG):
  https://github.com/yarnpkg/yarn/issues/786

* Support development using VS Code Remote Container

Co-authored-by: Kyle Doherty <5248953+kdoh@users.noreply.github.com>