fix a stupid coding problem in DownloadWorker parseJob
fix a small issue that the filename extension is wrong
Adding local storage cookie support, so that the user no longer need to retype the username
and password every time they open the program.
Right now the current stage is not complete.
the _load_cookie method has some bug that will cause the program crash.
Add several method that is responsible for checking wether we have a forum cookie or not,
But its not qutie stable so do not use it yet in the subclass.
Add a method to check wether we have successfuly login or not.
An enhancement for issue #4