[4.1] Make header classes configurable

[martijnb92]

While adding some offset classes to the content I noticed the header was no longer aligned. This PR adds the ability to define classes for the CRUD headers, usefull when working with content offset or any other classes you might need. By default they are the same as the content classes minus .bold-labels

[scrutinizer-notifier]

The inspection completed: 11 updated code elements