Streamline production build for Jenkins

This PR separates our dependencies into prod and dev. This will help make Jenkins deploys faster.

Before we deploy this we need to change the Jenkins config for both our production jobs so that they execute `npm i --production` shell command instead of `npm i`. This will stop Jenkins from installing all the testing stuff we have which takes a loooong time to install.

We also need to change the build task to: 

```js
grunt build --env=production
```

Lastly there is a PR for marketing-deploy to add the environment to the build task: https://github.com/optimizely/marketing-deploy/pull/21