Add: set transformation for people tracker

This patch series contributes to the PCL people tracker:

- the possibility to define a transformation matrix for cases where the people tracker coordinate frame does not fit the user coordinate frame is added. The transformation will be applied to the point cloud, the ground plane and the intrinsics matrix. The main rationale behind this feature is twofold: first, it simplifies the use of the people tracker. Second, the transformation can be applied after downsampling and thus is faster than it would be if the transformation would be done outside the people tracker.

- a bug related to calculating the minimal and maximal person cluster size is fixed

- some minor stuff