A simple alarm clock application

##functions:

The main function is timer for 10 minutes, 20 minutes and 30 minutes.

The layout should be 3 button and a updating window:

1. click the buttons of 10 mins etc. to set the timer.
2. the window of remaining time should update real time
3. when a timer is activated, click any button would reset the timer to new time

##Language: Python

##dependency: PyQt

##Environment: Windows