Decouple camera_node GUI and camera logic

[camera_node](https://github.com/ATR-Lab/coffee-buddy/blob/main/coffee_ws/src/coffee_vision/coffee_vision/camera_node.py) is a monolithic. It couples both the logic required to stream and do face tracking, and a PyQT GUI. Decouple it so that we can improve the performance of the node and be able to run it headless. 
