added class Storage. use storage to load from file and save to file
edited Task class to enable program to scan from textfile and convert everything to observblelist
added ModelTaskToSaveStringConverter to convert a modeltask to string for saving to file.
added time standardizing functionality
removed undo redo from storage because it's handled by commandfactory
modified the code to add in task converter to convert task to Modeltask
Merge remote-tracking branch 'origin/yongkai'
Merge remote-tracking branch 'origin/jiashun'