TOT-89 Better support for working offline (part 1/2)

This MR introduces some changes for TOT-89's task, but not all of them.

This MR introduces many changes to provide better support for working offline (also on mobile as an "app" (PWA)). Main changes in this MR are:

• automatically add a badge after creating alerts in device (local storage when offline)
• automatically upload alerts when back online: show a feedback to the user for each alert being uploaded
• show a wifi-off-icon when offline (and disable the menu)
• show user's first name at top left menu-bar
• fix PWA support (add default service-worker.js)
• don’t let users edit/delete alerts when offline

To test in the browser you can check the "Application" tab in the browser dev tools (in chrome there is the "offline" checkbox). To test in mobile you need to access via mobile web browser and then click "use as an app", or "add to homescreen" etc. (please contact me to double check which version is deployed in DEV environment).