Implemented save, load on open, and remove

ControlPanel
 - changed constructor to include a reference from the FileHandler
 - added ActionListener case for "delete" button and save function at
the end

Entry
 - fixed a string reference not being updated in the parseMonth method

FileHandler
 - changed separator character to '='

Lister
 - added the delete method

MainWindow
 - added FileHandler object, updated ControlPanel constructor call