[TASK] Namespaced classes

Resolves: #54620
Releases: 6.0,6.1,6.2

Change-Id: Ie20d3225acee5a948fce625ee8f844eee9be9fb2
Reviewed-on: https://review.typo3.org/26572
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen