GTK: adjust to new LIB API and refactor file error handling

This restructures large parts of the GUI-wise error handling code
and makes it more fine-grained, so the user can react appropriately
to exceptions.

src/HSFM/GUI/Gtk/Data.hs

@@ -35,8 +35,8 @@ import HPath
     Abs
   , Path
   )
-import HSFM.FileSystem.FileOperations
 import HSFM.FileSystem.FileType
+import HSFM.FileSystem.UtilTypes
 import System.INotify
   (
     INotify