Round values on the front end side with a fixed amount of decimal digits
using `Number.prototype.toFixed()`. Also adds unit to the weight delta
string.

Resolves Round values in frontend #112

* Fixed header
* Fixed sidenav on big screens
* non disruptive preloader
Problems:
* Scrollspy (sidebar nav) doesn't work
* Janky layout i think tbh xD
* Preloader not very noticeable (add "spotlight" effect?)
* You can open multiple different modals at once

You can choose if you want to save the to date
The rest gets saved and restored automatically
TODO: Add delta-timespan when ready

Use smooth scroll behavior when scrolling to an anchor using a link in
the navbar.

- Unset localStorage items if user opted-out
of localStorage using checkbox
- Add global variable 'saveInLocalStorage' representing whether
or not settings are supposed to be saved in localStorage
- Fix issues with seperate scale switch for weight in compare chart

Change weight unit to grams as that's the unit returned by the API.

Front End: Change Weight Unit to Grams

This reverts commit 0f7c81d.

Works for me in Firefox and Vivaldi

…rage

Front End: Now saving settings in local storage