Update the copyright date to 2021 in the headers of every source files

• Update to 2021
• Open ticket for 2022 and link it to this one

changed due date to December 18, 2020

changed milestone to %0.9.0

added Project label

changed the description

mentioned in issue #252 (closed)

marked this issue as related to #252 (closed)

changed the description

added Easy pick label

changed the description

marked this issue as related to #365 (closed)

marked the checklist item Update to 2021 as completed

marked the checklist item Open ticket for 2022 and link it to this one as completed

mentioned in commit 5f741ea0

closed

assigned to @moul