Attempt to move windows into nearest spaces when dropping them.

[Alysander]

At the moment when you move a window it will first attempt to place it in the nearest location.
If that fails, it will try to make the best fit it can.

I think it needs to trade off between these two things and first identify if the window is almost
the correct size for a nearby overlapping space and fit it into it.
A good heuristic will be needed.