Fix minor issues and remove depricated usage of cumulant LB method

Fixes some minor issues in the documentation and Assignment creation. Furthermore, the deprecated usage of the cumulant method is removed.

changed title from Incompressible cumulants to Fix minor issues

changed title from Fix minor issues to Fix minor issues and remove depricated usage of cumulant LB method

changed the description

resolved all threads

approved this merge request

merged

mentioned in commit 91a0cfad