Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, assimp team".
Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, ASSIMP Development Team".
Changed copyright end year to 2020 in LICENCE.rtf.
Changed copyright end year in CMakeFiles.txt files and any other places referencing Assimp with a copyright start and end year.
OptimizeGraph postprocessing now reverses face order when
node scale is mirroring.
Fixes flip to backfacing in models that mirrored some nodes.
(Odd count of negative scale components, negative determinant)
