URDF describing gazebo settings and frame transforms are coupled

[oswinso]

Right now, our jessii.urdf.xacro couples together gazebo settings, ie. https://github.com/RoboJackets/igvc-software/blob/7b91e36c1b24f750758758cb44a0fd900de1f687/igvc_description/urdf/jessii.urdf.xacro#L198-L201 https://github.com/RoboJackets/igvc-software/blob/7b91e36c1b24f750758758cb44a0fd900de1f687/igvc_description/urdf/jessii.urdf.xacro#L487-L492

as well as normal joints, ie.

https://github.com/RoboJackets/igvc-software/blob/7b91e36c1b24f750758758cb44a0fd900de1f687/igvc_description/urdf/jessii.urdf.xacro#L524-L529

Ideally, the two would be decoupled, so that robot_state_publisher for example only knows about the normal joint transforms, while gazebo would launch another .xacro which would include the gazebo specific ones, as well as including the normal xacro describing the joint transforms.

This also clears up arguments, as right now robot_state_publisher has access to a gpu argument that does nothing, which may make things confusing.