Disable precompilation of PPFRegistration

This fixes #906 by partially reverting #891.
Merge pull request #907 from taketwo/fix-906

Disable precompilation of PPFRegistration
Add Ensenso support in CMake files
Add Ensenso grabber example
Add EnsensoGrabber class
Add Ensenso simple viewer
Add Ensenso documentation & tutorial
SANDBOX
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