Add support for 'cache then network' strategy (PWA)

Is your feature request related to a problem? Please describe. Yes, in order for us to be able to work in a PWA environment, we need a service worker that would update as we update the codebase so the patches made can be live.

Describe the solution you'd like Employ 'cache then network' policy. Here's the material for reference https://developers.google.com/web/fundamentals/instant-and-offline/offline-cookbook#cache-then-network

Describe alternatives you've considered Would like suggestions for a different approaches as well to support the above functionality in a PWA environment.