Only reset window state if window is iconified
Add Timer window
Implement TimerModel
Implement TimerView
Add ConfigureNotificationAction
Fix bug: NotificationButton displays wrong text

setNormalText and setNotifyText modified the wrong variables.
TimerView starts the Notification when the timer finishes
Add StartCancelAction
Add PauseResumeAction
Fix bug: TimerView formats time badly

Improves the formatting of the time in the TimerView. The hour field
displays now 0 instead of 24 and a fraction of the second is included.
Finish timer feature
Fix bug: Application closing too early

The application closed too early sometimes and not with the last open
window.

This was caused by windowOpened() of WindowListener only being called
the first time a window is shown.

Unfortunately, because of this, CloseApplicationWindowListener can't
keep track of the number of open windows using an integer any more. It
has been changed to keep a list of windows and check how many are still
open every time windowClosing() is called.

Fixes #1 on Github.