Simplify Launch Files for Different Worlds

Currently we have essentially duplicate launch files for different environments other than the name of the launch file, e.g. grasp_scene.launch, emtpy_world.launch, and pick_and_place.launch these could easily be swapped out for a single environment loader launch file with an argument to select the environment.

This would allow the environments to still be loaded with different robots but simplify the maintenance of these files.