Enhancement: Streamline UI sizings

We've streamlined the font sizes and some other size related options to let the web UI appear a bit more condensed. In addition to that we've chosen a new font family for the UI ("Inter") which is embedded into the ownCloud Design System by default now.

https://github.com/owncloud/web/pull/7363
https://github.com/owncloud/web/issues/7333
https://github.com/owncloud/owncloud-design-system/pull/2270
