Can't run prod build using --omit=dev

[CharlesNadolski]

As a DevOps resource behind corporate firewall, npm install routinely times out due to test and dev dependencies (particularly cypress, which is a very large dependency). We would like to use npm install --omit=dev before running npm run build:prod to either build our own docker image or to deploy to a static web content PaaS.

The fix appears to be straightforward. In package.json move packages from devDependencies to (prod) dependencies which are not related to testing, linting, or dev tools.

I can provide a PR for this shortly, but I wanted to document the issue first.