Feature request: Sticky items

[demiro]

REQUIRED: Before filing a feature request

Change each [ ] to [x] when you have done it.

• [ x] My issue title starts with [feature request]
• [x ] I have thoroughly read through the README, and the dragula docs.
• [x ] I have searched through the ng2-dragula issues for related problems, including closed issues, and I didn't find anything.

Is your feature request related to a problem? Please describe. I have two lists and I move items from one to another... but there are some items inside that I want them to be fixed on top. I already implemented that they are not draggable by checking class "fixed" on start dragging. But how do I prevent it(them) to be reordered?

Describe the solution you'd like Would be great if I could set a directive to the specific items I don't want to be draggable nor sortable... so when shifting items around they would be fixed in their place