Separate the API and UI into two distinct services

[kenellorando]

The Cadence API server currently runs a Go fileserver which serves raw HTML, CSS, and JavaScript. It's simple and looks fine to me, but I think it's time we separate the services. As the number of API calls grows, so too does the management of the raw UI components built by hand that drive the frontend.

Separation might help for a potential UI overhaul using a modern JavaScript web development framework. Possibly with Vue or Svelte. Whatever it is, we want it to be easy to re-implement a theme changer. Present v5's UI is built with the Bulma library which is simply too difficult to style with pure as in pure CSS. Additionally, separation of services would allow the API and UI to be deployed and scaled independently.