[WIP] Fix/use default avatar lib

WIP because plugin will have to be addressed

https://www.openproject.org/work_packages/13706
https://www.openproject.org/work_packages/14688
https://www.openproject.org/work_packages/14701
https://www.openproject.org/work_packages/14814
https://www.openproject.org/work_packages/14690
@ulferts `nil` or empty? – these examples are failing.