Updated ros-pkg for RTAB-Map 0.8.0

Moved all nodelets and rviz plugins in "rtabmap_ros" namespace instead of "rtabmap"
Refactored rtabmap_ros messages (added convenient conversion methods in rtabmap_ros/MsgConversion.h)
Added noise filtering parameters for map_assembler node
Added variance parameter for map_optimizer node
Odometry nodes publish covariance matrices in odometry messages. Publish rtambap_ros::OdomInfo topic too.

msg/OdomInfo.msg

@@ -0,0 +1,21 @@
+
+Header header
+
+#class rtabmap::OdometryInfo
+#{
+#    bool lost;
+#    int matches;
+#    int inliers;
+#    float variance;
+#    int features;
+#    int localMapSize;
+#    float time;
+#}
+
+bool lost
+int32 matches
+int32 inliers
+float32 variance
+int32 features
+int32 localMapSize
+float32 time