Preview pane for folders

[KristofKekesi]

Describe the solution you'd like
Some additional informations about the folder (like how much sotrage does it take, how much files does it contain, or how much files with x file extension).

[yaira2]

@KristofKekesi This enhancement was implemented with #3639.

[winston-de]

Unfortunately, Folder previews were not finished in #3639, and were disabled.

I made a new PR where I will continue work on implementing this, #3773.

Also, here's what folder previews look like so far.