Added Notification when pomodoro is finished.

	App now displays a notification when the pomodoro is finished.
	Until now nothing happens when the user clicks on it.
Added sound to notification
Outsourced the timer into a new class PomodoroTimer

	Created a new class PomodoroTimer which extends CountdownTimer.
	It know which project is worked on and will later also be
	responsible for the breaks
Finished pomodoros now update the count on their project.

	After a pomodoro is finished the pomodoro count on the
	project the user has been working on is updated.