Unfortunately UITextEdit is really bad in terms of performance. It
cannot be used as overlying widget (just like in terminal). On the other
hand we could optimize it by rewriting (unfortunately) the whole widget.
There still is a lot of things to do, but for now it is possible to
select several lines of text and copy it using CTRL + C. In order to
make text copyable in context menu it will be required to override
onMousePress (return true).