[ROS][api][refactor] Add new package to perform driver point type conversion

By now, LidarSlamNode carries out a conversion between Velodyne driver point type (currently hold in velodyne_pcl/point_types.h) and the point type used in SLAM (LidarPoint.h).

1. Goals

• Make LidarSlamNode independent of the device used
• Create an independent conversion node specialized for Velodyne points input
• The new node must supply a PC2 msg which is directly convertible with LidarPoint.

2. Changes

• Create new topic lidar_points to supply pointclouds to LidarSlamNode
• Add new package for all needed drivers
• Add new Velodyne converter node
• Adapt LidarSlamNode consequently

@nicolas.cadart @nick.laurenson PTAL