message: rtabmap.launch: added gen_cloud option
diff: <arg name="rgb_image_transport" default="compressed"/> <!-- Common types: compressed, theora (see "rosrun image_transport list_transports") -->
  <arg name="depth_image_transport" default="compressedDepth"/> <!-- Depth compatible types: compressedDepth (see "rosrun image_transport list_transports") -->
  + <arg name="gen_cloud" default="false"/> <!-- only works with depth image and if not subscribing to scan_cloud topic-->
  + <arg name="gen_cloud_decimation" default="4"/>
  + <arg name="gen_cloud_voxel" default="0.05"/>
  +
  <arg name="subscribe_scan" default="false"/>
  <arg name="scan_topic" default="/scan"/>
  - <arg name="subscribe_scan_cloud" default="false"/>
  + <arg name="subscribe_scan_cloud" default="$(arg gen_cloud)"/>
  <arg name="scan_cloud_topic" default="/scan_cloud"/>
  <arg name="subscribe_scan_descriptor" default="false"/>
  <arg name="scan_descriptor_topic" default="/scan_descriptor"/>
  </group>
  </group>
  + <node pkg="nodelet" type="nodelet" name="gen_cloud_from_depth" args="standalone rtabmap_ros/point_cloud_xyz" clear_params="$(arg clear_params)" output="$(arg output)">
  + <remap from="depth/image" to="$(arg depth_topic_relay)"/>
  + <remap from="depth/camera_info" to="$(arg camera_info_topic)"/>
  + <remap from="cloud" to="$(arg scan_cloud_topic)" />
  +
  + <param name="decimation" type="double" value="$(arg gen_cloud_decimation)"/>
  + <param name="voxel_size" type="double" value="$(arg gen_cloud_voxel)"/>
  + <param name="approx_sync" type="bool" value="false"/>
  + </node>
  +
  <!-- Visual odometry -->
  <group unless="$(arg icp_odometry)">
  <group if="$(arg visual_odometry)">
  