Added Droppable

I needed a droppable target that would add items to an observable array without a sortable. Using the seating chart sample, it would allow you to drop students on table names with out having any template/child elements.

connectClass, beforeMove and afterMove, options, isEnabled all work the same (connectClass set's the droppable's accept)

An additional property, targetIndex, specifies where to put the new item, by default (null) it is appended. You can safely set to 0 to put at the start, or set it in beforeMove.

Every once in a while, I see a "Cannot call method 'removeChild' of null " on the source placeholder. Not sure what that is about, timing maybe. Appears to be this issue with JQuery UI: http://bugs.jqueryui.com/ticket/6054 

Brian
The above code tries to do something if the data valueAccessor is an ObservableArray (or any other Observable having the splice method), but doesn't do anything if the data is a simple Observable.