Black screen the front-end when fail

This is connected to issue #9. The system send a signal to front-end when there is failure in the pellet dispenser.

• When pellet dispenser feedback signal is detected, the back-end system should send a signal to the front-end to set a blackscreen.

Purpose

The purpose is to avoid the monkeys to use the application when there is a failure in the pellet dispenser.

Definition of failure

The system will interpret that there is a failure when the pellet dispenser is empty or there is something stuck in it.