Test and build execution: use npm ci

[zven]

@jbraese realized, while working on #158, that we are using npm install for our automated build, test and deployment processes. To execute those with a clean install, it's advised to usenpm ci instead: https://docs.npmjs.com/cli/v8/commands/npm-ci

[felixerdy]

I think we should first investigate #166 (comment) in #166 as npm config set package-lock false installs different versions of packages (which you can see in the /src/assets/licenses.json file generated in the postinstall script). Other than that npm ci works fine for me and also triggers the postinstall script which is nice.