Support increasing/decreasing font sizes via browser settings

[LukasHirt]

If a user sets bigger or smaller font sizes in the settings of his browser, the changes should be also reflected in the web UI.

[LukasHirt]

Needs to be taken care that the layout is also not completely broken when that happens.

[Deaddy]

We also ran into this issue. Currently I need to zoom out to 60% until I can use the webinterface without issues to my visual system, but at that point some things already start to become blurry.

While not as nice as respecting the browser's choice, a (cookie based) larger/smaller-Fontsize button in some corner might also work, especially for those users who are not familiar with their browsers but still need to accomodate their fontsize, but maybe this is something for another issue.

[kulmann]

Respecting the font size set in the browser has been implemented in #7363 - we scale the browser font size down to 88% and use that as base font size for all font size related css classes / stylings. Works pretty well for me. Happy to get feedback to improve this further - please reopen this ticket as needed.

Also, @Deaddy the linked PR reduced the UI sizings quite a bit, so that the UI doesn't appear so clunky anymore.