Create urdf.xacro file for Gigatron with race body

[5yler]

The current gigatron.urdf.xacro has sensor mounting and car dimensions specific to the test hardware mounting without the race body.

Tasks

• [x] modify imu_link with final IMU mount location for race
• [x] modify laser_link with final RPLIDAR mount location for race
• [x] add back_laser_link if using a second LIDAR mounted on the rear of the car

[5yler]

Approximate location of front LIDAR:

• 8" in front of forward axle
• 9" above axle

Rear LIDAR:

• 7" behind rear axle
• 12" above axle

IMU:

• center of base_link along x and y
• height TBD but on bottom of body

[DJGCrusader]

DONE