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 warnings in OpenNI 2 grabberModeToOpenniMode

* Fixed assignment in conditional test
* Removed unused argument to focal length getters
* Removed 'register' keywords that do nothing.
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.
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.
Refactored obscure kinfu app function names.
Fixed confusing names in kinfu app.
Split kinfu operator(..) into trackFrame(..) and integrateFrame(..)
Added forcedPose kinfu integration.
Separated out ICP tracking from saving the pose.

* Can check for tracking sanity before integrating the frame data