[camera] No self.__class__ in super()

Which can lead to recursive call
[sensor] add Kinect w/ROS XYZRGB PointCloud2

Factorise intrinsic matrix code of DepthCamera in VideoCamera.
Change boolean property "Depth" to "retrieve_depth".
Add C module to compute real Z range from OpenGL depth buffer, without
XY which can be retrieved with intrinsic matrix. This will be useful
for ROS Kinect simulation later on with the depth_image_proc package.