Textures were being double deleted after a merge scene because the
texture array wasn't being properly deleted at the end of merging.
Furthermore, the texture array was being sized to the number of
materials instead of the number of textures.
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.