Modified filter chain for rotunit

- Added 'kurt360_laser_filter.yaml' which contains parameters for laser shadow filter;
  this is a preparation for separation of laser and scan filtering and thus allow for a real
  self-filter
- Replaced scan_to_scan filter with a scan_to_cloud filter
- Added a self filtering for point clouds
- Replaced laser_scan_assembler with point_cloud2_assembler and provided self filtered
  point clouds as input
- Removed (now obsolete) file 'kurt360_laser_self_filter.yaml', since the laser filtering
  has been moved to 'kurt360_laser_filter.yaml' and the self filtering is done via
  'kurt360_self_filter.yaml'