Unbreak drag drop of tabs in wayland

This makes tab drag drop to work, but it creates a few annoyances
that I was unable to solve:

The drop outside is behaving in an weird way: as soon as it's dropped
nothing happens but when the mouse get's back to the window, the new
window will then appear. the exec() method of the drag will *not* finish
when the mouse is released outside of the widget that started it, for some reason

The movement of the tabbar is broken if you first rearrange the tabs then
dragoutside. A click on the tabbar fixes it, but a fake click using a fake
event does not not do anything.

Still, better than a non working drag drop on wayland