add IMU and Laserscanner xacro

[padhupradheep]

Make it available as options to the users, depending upon their needs they can select. It should be a launch argument, which would then be explicitly converted into a xacro argument, and passed on to the urdf.xacro of the robot,

• S300
• IMU

Create individual xacros for laserscanners and IMU. Can be as flexible as it can.