Allow the drop to be cancelled

[rojtjo]

Hi there,

First of all thank you for making this great component!

I'm building a component to manage (nested) menu items and use your component to handle the sorting of the items. In my use case I needed to be able to cancel a drop if the level is greater than a certain number.

In order to do this I added an additional event (beforedrop) which is fired just before a drop is handled. It sends the same data as the drop event except that the native event is replaced by a cancel function. Once the cancel function is called it will halt the execution of the drop.

Let me know if you'd like me to change something or add documentation for it.

Cheers,
Roj

[holiber]

Hi, thank you for PR.

[dadigu]

Hi, when will this feature be tagged in a new release? I could really use this 👍