Implement offline experience

[addyosmani]

From @devnook

I'd like it to be our "offline strategy" take, like a Downosaur or a PWA offline crossword from Guardian, as in "hey, you have no connection, but you can at least play this!". We could touch a bit on PWA offline responsibility point, e.g. that it's not a great idea to save ALL the doodles to the user's device memory.

I like this idea. We just need to remove the links to the game from the main navigation and setup the particular path as what we offline. We still need to add in Workbox somewhere to accomplish this.