sfm: move to applications/file-managers

pkgs/top-level/all-packages.nix

···
 
   nnn = callPackage ../applications/misc/nnn { };
 
-  sfm = callPackage ../applications/misc/sfm { };
+  sfm = callPackage ../applications/file-managers/sfm { };
 
   shfm = callPackage ../applications/misc/shfm { };