Description:
 an abstract class that walk recursively through a given path.
 Activating the walking can be done by calling the StartWalking($pathtofolder) function
 This class contains 4 abstract function that the user needs to implements:
 1. FolderFilter: a function that will be called when walking process finds a folder. Expected to return true of false
 2. ProcessFolder: a function that will be called if FolderFilter function returns true
 3. FileFilter: behave the same as FolderFilter but instead of folder, this function subject is file
 4. ProcessFilter: a function that will be called if FileFilter returns true

Todo: repair the $mStringFolderTree. It still didn't print the tree of the folder correctly 

License: LGPL