Allow tabs to be dragged and dropped between windows

[tyzoid]

Currently, tabs can only be moved by the use of a move or "paste" button. This will move the tab to the current window.

Sometimes, however, if I'm reorganizing my tabs, I will want to move tabs between two windows which are not in focus - a common task, for example when doing web development or reading documentation.

[moosingin3space]

I believe the use case is worth implementing this functionality. Probably a few more minor releases away.