[CLEANUP] Cleanup various domain model classes

* import classes
* remove superfluous comments
  * reason explained here: http://forge.typo3.org/issues/58248#note-1
* use spaces in string concatinations
* Improve some vertical rhythm by using some vertical space
* Support method chaining not only for some of the methods in a class
* remove superfluous empty lines

Resolves: #58256
Releases: 6.2
Change-Id: I47c0bc9d4d12b1fcc8e0a96f5c74245e4e732e36
Reviewed-on: https://review.typo3.org/29686
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen