Added Edit command in OOP
Merge remote-tracking branch 'origin/yongkai'
Changed usage of ArrayList to ObservableList.
Changed usage of Task to ModelTask.
Added Search command in OOP
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.