[TYPO3-core] RFC #16626: Improve ExtJS grid styling

[Steffen Kamper]

Hi,

+1 by reading and testing.

Committed to trunk rev 9715

Some additional notes, could be done later

* is this wanted that the expanded arraow is black and the collapsed 
arraow grey? This is different to other places eg module menu
* the red arraow for sorting no is clean, but anyway i think it should 
change - i can't identify if its arrow up or down

vg Steffen