draggable.DragZone: register main thread configs

The current logic is too complicated, especially in case there are multiple drag zones in use.

E.g.:

    afterSetScrollContainerId(value, oldValue) {
        if (value) {
            let me    = this,
                owner = me.owner,
                listenerId;

            if (owner.mounted) {
                Neo.main.addon.DragDrop.setScrollContainer({
                    id: value
                });
            } else {
                listenerId = owner.on('mounted', () => {
                    owner.un('mounted', listenerId);
                    me.afterSetScrollContainerId(value, oldValue);
                });
            }
        }
    }

This approach forces each drag zone owner to set & reset the related main thread configs on drag:start & end.

Instead, each drag zone should send the relevant main thread configs over onDragStart() and the main thread addon needs to reset them on drag:end.

there should be a method like "getMainThreadConfigs" which child drag (&sort) zone classes can extend.

looking into this now.