[io] Add PCL grabber for ZED Stereo Camera

ZED Stereo cameras have become quite popular and used by quite a lot of people. Adding its support would be a great feature to have.

Context

Currently, OpenNI and RealSense devices are only supported by PCL. It makes sense to have ZED too, it's as popular as the above two. It would be great if we could have a standard API to access all these devices. Usage of these devices through this API would reduce redundancy and help avoid bad practices that are inherent when users try to write their own grabber.

Expected behavior

Similar to current implementations of OpenNI and RealSense devices. ZED already has examples to get started with this.

Current Behavior

Doesn't exist. Have to write your own grabber using ZED API.

Describe the solution you'd like

A wrapper over ZED API having an interface similar to wrappers for existing devices.

Describe alternatives you've considered

One question that comes to mind is slightly opposite to the proposed idea is that, do such wrappers need to exist or should be removed from PCL and be left to the respective manufacturers to provide interfaces and users write their own wrappers, instead of bloating PCL.
Maintaining such a codebase is also an issue as it requires access to physical hardware.

Compare the existing OpenNI and RealSense device wrappers with the ZED examples, especially depth sensing/cpp/src/main.cpp. First determine whether PCL should maintain another hardware-dependent wrapper or leave this to the manufacturer; done would require an agreed interface and a working ZED grabber matching the existing implementations.