Tabbar - use IconButton instead of icons for navigating through tabs

[larserbach]

The tabbar currently uses icons on the left and right to navigate through the tabs.
A iconbutton should be used here instead.

In case props were changed: Props Excel has been updated / comments have been resolved and props changed from red to black font color > @thrbnhrtmnn or @angelicahoyss can support here

[thrbnhrtmnn]

Hey @larserbach , I moved this to the next iteration, as this was not initially planned. If there is a good reason why this needs to be done in this iteration, let me know :-)