Bug fix for folderlistmodel

If you have used folderlistmodel in Qt.labs.folderlistmodel 1.0, I am sure that it will make you disappointed because it cannot reflect the change from system file such as file deleted, file renamed, ...
I found that folderlistmodel is based on QDirModel which is a deprecated class. I decided to implement it again using QFileSystemModel because QFileSystemModel use file system watcher.
I have succeeded!If you have same problem as me, drop me a line...