Fixed data race problem with multiple sensors

* The convertTo..PointCloud methods used statically allocated buffers to resize images, causing a data race if multiple deices tried to create point clouds simultaneously. Switched to using member buffers for each grabber.
Removed throwing exception on frame sync failure.

* This is not an exceptional event. Print error message instead.
Removed unused class members.

* Focal length calculation now done with FOV data from OpenNI and not cached.
Simplified OpenNI library search paths.
Added getter for image step (row stride).
Removed get[..]Stream() calls and added triggerSingleFrame(..)
Added single-frame triggering.
Merged shutdown(..) with ~OpenNI2Device(..)
Fixed abstraction around existing OpenNI 1.x grabber.

This should help with switching between OpenNI 1.x and 2.x grabbers.
Added fall-through to OpenNI 2 grabber.

If OpenNI 2 is being used, have openni_grabber.h include openni2_grabber.h.
Enabled kinfu CMake option with OpenNI 2.
Added OpenNI2 library checks when building kinfu app.
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.
Refactored obscure kinfu app function names.
Fixed confusing names in kinfu app.
Split kinfu operator(..) into trackFrame(..) and integrateFrame(..)
Fixed Clang warnings.