Reworking the kwin tabbox

[Jacopo De Simoi]

> Comments and espicially help on implementation are more than welcome.

We already have a staticQueryMode for user switching; we could perhaps add a 
"simpleQueryMode" with just a LineEdit without history (of course) and the close button, 
with queries restricted to a single runner, which will in this case be the kwin runner;

As for thumbnails, we would need more hacking here and there but that should be do-able

Of course I'll be happy to help substantially to implement this idea, spare time permitting.
Best wishes

 Jacopo