Display information on selection, bug fix

- Clicking on an event will now display the 
information in the fields

- Fixed bugs relating to empty title or memo fields

Changes:

ControlPanel
 - moved empty date rule inside "add" button
action listener and exited method on it

DateEntry
 - changed constructor to convert "" to " "
for title and memo

Lister
 - added ControlPanel object
 - Detect no selection on delete and exit method
 - added selection update behavior to 
DisableSelectionModel class

MainWindow
 - passed ControlPanel object to Lister

Todo:
Adjust fields for ease of adding new entries
after a selection has been made.
Possibly autoselect all text in each box on selection