Configurable simulation worlds #52

The simulation has three fixed worlds, chosen by a path to the world file.
Add a kpi_rover_worlds package with configurable worlds (garden, maze, overpass, test square): arguments such as floor and marking, named start points, and previews for tools such as the GUI. sim.launch.py takes a world by name, its arguments and a start point. The package is for the simulation only, not for the robot image.