Vanilla HTML form for COVID calculator

Instead of using a voila dashboard for the COVID calculator, we have chosen to use a simple HTML based form, with a RESTful endpoint to return the model results.

In order to achieve this, we need the COVID calculator wireframe (from #4 (closed) and #33 (closed)) in a HTML form. You can use any framework you like to build the form, suggestion of jQuery was made and would be a reasonable choice. Bootstrap for styling may also be a good option. Whichever technology works best for you is the best choice here - we can always adjust after the short deadline if necessary.

The data to be sent over to the REST endpoint at /calculator/api/calculator is to be agreed in (#37 (closed)).