Realistic Gazebo Simulator World

[maxsvetlik]

This adds models for GDC 3ne for use in Gazebo sim. These models were built off of a real-world SLAM map using Gazebo's building editor tool.

The number of walls and how they're specified (sdf vs mesh) means that the simulator has more to deal with and runs at a lower frame rate in the realistic world. It should be more accurate, however.

This has not been integrated as a replacement for the existing de-facto Gazebo simulator world in this repo, since the existing world may still be useful to compare against as it has been used in previous experiments and papers.

[maxsvetlik]

This is working in Kinetic with a single robot instance, i.e. launching simulation_v2.realistic_gazebo.launch. Unfortunately this does not scale to multiple robot instances in Kinetic, as Gazebo fails to load odometry plugins for n-1 robots. This seems only to happen if the world file includes models that have 'too many' links. So a multi_robot_simulation.realistic_gazebo.launch will not work as expected in Kinetic because Gazebo does not publish the odom information that's required for our stack.

Fortunately this is not an issue in Gazebo 9 in ROS Melodic, and works right out of the box. So I guess this is blocked on the upgrade to Melodic.