Don't drag windows in empty areas from touch/pen events
For a mouse users have the precision that if they clicked in an empty
area they want to perform some action.
For touch and tablets that isn't necessarily true.
From Boud in a kwin report: "The drag the window by empty areas is a
nasty one as well, especially when you're using a pen."
Change needs to happen in oxygen too
Moved window using sidebar of kate with mouse
Couldn't drag it with a pen
Differential Revision: https://phabricator.kde.org/D15942