Fix initial loading (see issue) and dispatch a dragging event (because we are cancelling the original)

[yorrd]

Well, since this might not be the only possible solution, I'm going to share the problem I'm trying to solve: I want to

1. know when any element on the page is dragged and therefore catch some form of track event from Polymer
2. not removing the stopPropagation again, because then nested the-grids don't work anymore

So I made up this custom event which I'm currently using in my local branch of this component. If you have another better idea to solve this, let me know!