Open closed widget areas when dragging onto them

[mitchoyoshitaka]

Right now if you start dragging a widget in the widget admin and drag it over a closed widget area, you have to let go once, open up the widget area, then drag again. Make it so closed widget areas open up when you drag things onto them, perhaps after a slight (500ms?) delay.

I've had a look at the code and sorta got it working. There are two problems:

1. When dragging the closed widget holders don't open reliably. You have to drag the draggable item over the widget window title a whole bunch of times before it actually opens.

2. When hover-opened the widget holder won't accept draggables. I'm guessing that the closed widget holder isn't available when the sorting process begins and therefore isn't included in the list of places where stuff can be dropped.

If those two problems can be solved then this patch should work. Haven't built in any delay, though.