Add an API endpoint to add, remove or update ACLs
    
    This API endpoint allows any project admin to add, remove or update
    ACLs on the project.
    It supports updating ACLs for users and groups.
    
    Fixes https://pagure.io/pagure/issue/2747
    Merges https://pagure.io/pagure/pull-request/3417
    
    Signed-off-by: Karsten Hopp <karsten@redhat.com></karsten@redhat.com>