Offline with service worker

[electricg]

Things left to do or to check:

• in public/sw.js there is to define the list of files we want to be stored by default. I already added the functionality that any other additional file downloaded later is also added to the cache
• check if you like the visual effect to tell users when sw is activated and when there is a new version 😂 results of hours and hours on Photoshop 🙈
• check if I didn't do anything wrong or stupid

DON'T RELEASE IT before publishing the whole proper speakers list!!

[remy]

Do you want me to code review the service worker stuff? (ie. for learning and feedback).

Otherwise I've got a drop in solution for SW which works pretty reliably.

[electricg]

If you have the time to do a code review it would be awesome! But I am also curious to see your solution