Don't drag windows in empty areas from touch/pen events

Summary:
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

Test Plan:
Moved window using sidebar of kate with mouse
Couldn't drag it with a pen

Reviewers: #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D15942