message: rtabmap.launch: fixed imu_topic argument not used by rgbd_odometry
diff: <remap from="rgb/camera_info" to="$(arg camera_info_topic)"/>
  <remap from="rgbd_image" to="$(arg rgbd_topic_relay)"/>
  <remap from="odom" to="$(arg odom_topic)"/>
  + <remap from="imu" to="$(arg imu_topic)"/>
  <param name="frame_id" type="string" value="$(arg frame_id)"/>
  <param name="odom_frame_id" type="string" value="$(arg vo_frame_id)"/>
  <remap from="scan" to="$(arg scan_topic)"/>
  <remap from="scan_cloud" to="$(arg scan_cloud_topic)"/>
  <remap from="odom" to="$(arg odom_topic)"/>
  + <remap from="imu" to="$(arg imu_topic)"/>
  <param name="frame_id" type="string" value="$(arg frame_id)"/>
  <param name="odom_frame_id" type="string" value="$(arg vo_frame_id)"/>
  