Freezes when dragging on large amount of terms

[romanberdnikov]

Hi, thank you for the great plugin! However I found some issues when using it on a large number of terms (about 638 items).

1. At some point it starts to exceed the "max_input_vars" PHP param. It would be great to throw some error or make a notice in the plugin description.

2. It freezes for a 1-2 seconds after drag-and-drop. I think it would be a good idea to implement up and down buttons with a setTimeout being called. So the order saving starts after the user finishes with it