Merge tag 'v2.13.0' into develop

added material density + tests thanks to @wenqiushui v2.13.0

# gpg: Signature made Sat Nov 21 12:02:23 2020 CET
# gpg:                using RSA key 149325FD15904E9C4EB89E95E81444E9CE1F695D
# gpg: Good signature from "Rick van Hattem <[email protected]>" [ultimate]
# gpg:                 aka "[jpeg image of size 9662]" [ultimate]

Author: wolph