Control/Main Flow of Gazebo World Components

[JimmeeX]

Controls the Gazebo Environment (conveyor, robot, proximity sensor) based on triggers/inputs from other modules.
Specific functionalities are still vague.

Considerations

• conveyor_out should stop when a new order is detected by break_beam_out
• conveyor_out should start on trigger (ie, when the order is finished) [maybe requires a separate "order" node]
• conveyor_in should stop when a desired object hits the break_beam_in [requires cooperation of vision]
• conveyor_out should start when the desired object has been collected and put into the container, and the robot returns to the original position for collection [requires co-operation of motion]

[JimmeeX]

done #22