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.
Initially i used resize because i wanted to track the size of the internal vector (cloud->points), but then i decided to track it manually with
size_t numberPointsInCloud
This way i avoided a division by the cloud->point_step.
Nevertheless reserve is more efficient than resize, because doesnt insert default value elements, so i will changed it.