Various minor cleanups.

- Suppress deprecation in DropDownListBoxSelectionChangedEventSubscriber.

- Format javadoc in EndNotify.

- Remove useless comments, improve method parameter names, remove
  redundant casts to float, remove commented-out code, improve
  formatting in Falloff.

- Invert if clause in ImageModeHelper to return immediately if
  imageModeProperty in getAreaProviderProperty is null rather than
  surrounding the entire method's logic in an 'if imageModeProperty !=
  null' clause. Also return null in the else clause since before the else
  would simply fall through and return null at the end of the method
  anyway. Do the same with getRenderStrategyProperty.

- Add @Override annotations where appropriate and format javadoc in
  Screen.