add headless chromium software release

This change includes a rewrite of the previous component/headless-chromium, which used an outdated version of Chromium. It differs from component/chromium in that:

• It only provides a headless shell, rather than the full Chromium browser (though this can be changed).
• It compiles from source rather than downloading a binary build.

There is also a new software release software/headless-chromium which makes use of the updated component/headless-chromium to expose a remote debugging port.