Fixed abstraction around existing OpenNI 1.x grabber.

This should help with switching between OpenNI 1.x and 2.x grabbers.
Enabled kinfu CMake option with OpenNI 2.
Added OpenNI2 library checks when building kinfu app.
Added fall-through to OpenNI 2 grabber.

If OpenNI 2 is being used, have openni_grabber.h include openni2_grabber.h.
Disabled some kinfu classes that depend on OpenNI 1.x when OpenNI 2 is being used.
Masked oni_grabber errors when the OpenNI 1.x wrapper is not used.
Added conditional compile instead of changing OniGrabber cast type.

Should prevent regression problems when using OpenNI 1.x.
Disabled pcl_record_tsdfvolume when using OpenNI 2.