Adding bearing angle image to pcl

To represent a 3D laser point cloud in a more simplified way, a Bearing Angle(BA) model was employed to transform a 3D point cloud into a 2D image in pcl/bearing_angle, so that image processing methods can be used in many aspects.

Bearing Angle is defined as the angle between the laser beam and the segment connecting two consecutive measurement points (see Fig. 1). Grey values for a Bearing Angle image are proportional to the reflected laser light energy, which depends not only on how far away the measured object is from the scanner but also on the surface characteristics of the object.
![bearing angle](https://f.cloud.github.com/assets/3293366/824272/48530d92-f040-11e2-8209-24d03cce216b.jpg)
Fig. 1 The Bearing Angle is calculated along the diagonal direction