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

rtgui/CMakeLists.txt

@@ -161,6 +161,7 @@ set(NONCLISOURCEFILES
     labgrid.cc
     softlight.cc
     dehaze.cc
+    filmnegative.cc
     )
 
 include_directories(BEFORE "${CMAKE_CURRENT_BINARY_DIR}")