Added JS event for when the user changes the directory

This enables apps to detect directory changes which might be caused by
the user using the browser back button.

apps/files/js/filelist.js

@@ -170,6 +170,12 @@ var FileList={
 			return;
 		}
 		FileList.setCurrentDir(targetDir, changeUrl);
+		$('#fileList').trigger(
+			jQuery.Event('changeDirectory', {
+				dir: targetDir,
+				previousDir: currentDir
+			}
+		));
 		FileList.reload();
 	},
 	linkTo: function(dir) {