Build error DepthPacketProcessor is now internal

Hi
the project doesn't build anymore due to recent changes in libfreenect2.
I opened an libfreenect2 issue here: [https://github.com/OpenKinect/libfreenect2/issues/496]

The build error is 

```
kinect2_bridge.cpp:393:5: error: incomplete type ‘libfreenect2::DepthPacketProcessor’ used in nested name specifier
     libfreenect2::DepthPacketProcessor::Config config;
```

I use ROS jade. 
