[TYPO3-core] RFC: #11397: [Feature] Add class for render HTML header/footer for BE and FE

[Steffen Kamper]

Hi,

the latest thing i did was using abstract for the class. This means that 
you can't use an instance of the class, but you should extend it with 
your own class.
Because of that the unit test fails. I now use a foo class in unit test. 
It works, but i'm not sure if this is the right way for unit tests.
See attached tests.

vg Steffen