The push notification update

Description

In pomodoro mode, whenever the clock reaches 00:00, a push notification is sent to inform the user that the pomodoro or rest period has ended.

A new notification will be sent every 20 seconds until the user press OK within the application.

Fixes

• The application will now display an error message and exit if an unknown color is specified for any component.
• Error messages have been updated to be more detailed and descriptive.