Efficiency improvements and customizable occupancy 2D map projection.

+ Efficiency improvements:
|- avoid transforming clouds already in map frame (added additional
parameter to specify sensor frame_id for calculating sensor pose)
|- create occupancy cloud directly as ros message instead of pcl cloud
(avoids conversion)

+ Projection of nav_msgs::OccupancyGrid with customizable height and
initialization as free or unknown.

+ Increased tf listener buffer to 30 sec.
`m_sensorFrameId`  is used with its default value (empty string) if the user does not explicitly set it. This will break existing code / launch files. I would also discourage using a parameter for frame IDs since all incoming point clouds already have a valid frame ID.