Lost kwin tabs support

[nick87720z]

I remember, at least in 2010 or 2011 year qtcurve had tabs support. They had however own look. I propose to make them looking same as tabs. I have seen some options about their look in toolbar. Did not see, how it looks, but in this case header may be considered as toolbar and tab look could match tabs settings about tabs inside toolbar.

[MilesBHuff]

Yeah, having tab support again would be nice. 👍