Create a new "empty frontend" project

[bmonkman]

Related to #368 If someone wants to create a new frontend that is deployable into Zero infrastructure (using S3/Cloudfront) but doesn't want any of our existing frontend (React) boilerplate, there should be a very lightweight version that basically just has the CD workflows and a single HTML file with some inline javascript making an ajax call to the backend and displaying the result. It should be as simple as possible so as not to distract people from the main point, which is the stuff that can be copied to make a project compatible with Zero (in the case of the frontend, only CD pipeline) A totally empty repo has been added so it's able to be forked: https://github.com/commitdev/zero-frontend-empty