Film negative processing: first usable version. Only supports bayer raw files, thumbnails don't work

Added performance improvements suggested by heckflosse. Lowered median sampling step from 7 to 5 since calculation is now much faster.

Added support for Fuji X-Trans raw files.

Applied SSE2 patch provided by @heckflosse, improves performance in main processing loop.

Moved film negative processing stuff in its own compilation unit.

Code cleanup: removed redundant omp directives.

Added check for dead pixels, going above threshold after inversion. ST_BAYER only for now.

Reverted leftover hack in cropwindow.cc

rtengine/CMakeLists.txt

@@ -132,6 +132,7 @@ set(RTENGINESOURCEFILES
     ipdehaze.cc
     iplabregions.cc
     lj92.c
+    filmnegativeproc.cc
     )
 
 if(LENSFUN_HAS_LOAD_DIRECTORY)