portfolio-filemanager: move to applications/file-managers

pkgs/top-level/all-packages.nix

···
 
   ponymix = callPackage ../applications/audio/ponymix { };
 
-  portfolio-filemanager = callPackage ../applications/misc/portfolio-filemanager { };
+  portfolio-filemanager = callPackage ../applications/file-managers/portfolio-filemanager { };
 
   pothos = libsForQt5.callPackage ../applications/radio/pothos { };