Panel: show/filter translated content#344

I want to be able to quickly filter for content that has already a translation for the currently selected content language.
A label for the cards with the translated languages would also be a nice addition.
In an advanced version there could also be a “Delete content” button for the current selected language.

For now, you can use this plugin: https://github.com/junohamburg/kirby-language-selector

For the button: https://kirby.nolt.io/317