Add world button to ClockView

This button will later open the world clocks frame.
Add WorldFrame which will display clocks for different time zones

The WorldFrame is opened by a OpenWorldClocksAction instance.
ClockController initializes the actions and creates the newly added
TickController, which is the former ClockController.
Add ZoneSelectionDialog

This class will display a dialog asking the user to select a time zone.
Remove WorldFrame

WorldFrame is removed and the JFrame is created and configured locally
in the OpenWorldClocksAction. It also sets up a WorldModel and a
WorldController and connects them with the WorldView.
Fix bug: if minimized world clock frame does not show up if the button
is pressed