Finished separation of screens into classes

Next steps:
-Animation of movement between screens
-Undo/redo
-Alerts/confirmation messages
-Fix bugs
    -Editing *CLActivity*s
Animations added

Fixed minor bug:
-DataScreen scrolled when you were typing in the HTML field and pressed the spacebar
Addition of help hints plus miscellaneous changes

SUMMARY OF CHANGES

DataScreen
*Made 'scrollpane' a class variable
*Added a method to update the 'year' combo box

HelpHint
*<created class>

HomeScreen
*Changed text field default text to a prompt text
*Made file open immediately when file is selected in dialog, instead of populating text field with the file path

MainScreen
*Added help hints

Screen
*Creation of platform for help hints
**Boolean variables to control display of help hints
**Boolean variable to fix help hint problems when dragging window
**Added help hint button
**Added window button help hints
**Event handlers for hint button

Main
*Adjust layout of screens
*Close open file when user returns to home screen
*Updating of 'year' combo
*Implement help handlers
*Updates to default settings