Reordering stucks in some situations

[KristofMorva]

I don't know if these problems have any connection, so I only open one ticket. The problem is, in some situations we can't drag&drop like we could have some versions before. For example this item just cannot be moved one column to the left: Sometimes bigger items are not moving smaller items away while dragging, making it impossible to drop, and in rare situations you can place items above each other. Lastly, if you drag one item, you can keep pushing another item out in nowhere without limits. All of these can be reproduced easily on the main page of the official GitHub website (http://dsmorse.github.io/gridster.js/)