Improve tabs experience

[DavidMStraub]

We should migrate from mwc-tab to md-tabs (docs: https://material-web.dev/components/tabs/).

Also, to solve various issues with wrong tab indicators, we should consider using URL fragments for tabs (.../some-page#some-tab).

[DavidMStraub]

43f66fc removed mwc-tabs everywhere except the object view. But before investing work into object view tabs, I think we should reconsider the object view overall. Perhaps we can reduce the use of tabs.

[DavidMStraub]

Done!