Ui needs optimization for mobile screen sizes

[TimSchulzRC]

Even if the application might not be intended to be used on mobile devices, because the it is hosted as website, it should be optimised for all major device screen sizes used to browse the web (including smartphone and tablet sizes).

Since these days most internet browsing is done using smartphones (https://www.similarweb.com/platforms/), the application should either be accessible on smartphone screen sizes or at leas show a message that it is only available on desktop browsers.

As tablets are more and more used as a substitute for desktop devices, I suggest to optimise the ui scaling at least for tabled sized screen/window sizes (related to issue #8).

Scaling on smartphone screen sizes (using the screen size of the iPhone XR as a popular example):

Scaling on tablet screen sizes (using the screen size of the iPad Air as a popular example):