Make Buttons and Dropdowns Turbo 8 friendly

[Robin481]

Depends on this being completed: #752

Turbo 8 adds Link-Preloading. This works perfecty fine for normal links but not for e.g. The People dropdown because those probably aren't normal links. Some dropdwon libraries have a option to display the elements as links. Maybe ours has that.

TODO:

• Check which buttons, dropdowns or actual links that don't work with Link-Preloading yet
• Try to fix as many of those wherever possible
• Make sure performance doesn't become an issue (e.g. In the People Dropdown scrolling over "all" the people when looking through the list will then send a request each which might be a bit too much)