Obstacle in the octomap

[ivrolan]

This PR filters all the octomap nodes and deletes the ones below or at surface level.

Also some problems with the obstacle layer in the grid_map were detected. The function is_obstacle()started the raycasting from z=0,. Changed the function to raycast only 1 ray from z = surface + min_height to z= surface + max_height and return true if dist < max_height - min_height.

Additionally, some parameters of the maps were changed (e.g. min_height was lowered to show the robot in the apollo world)

Cheers, Iván López Broceño