Add draggableOptions option to jquery.gridList

## Need

We want to be able to customize the behavior of the jquery.draggable plugin 

## Deliverables

- [x] A `draggableOptions` option in the jquery.gridList lib that it passed to the jquery.draggable call

## TODO

- [x] add defaults for `draggableOptions`
- [x] extend the defaults with the given options and pass it to the draggable constructor
- [x] document this

## Notes

The `draggableOptions` defaults should be:
- `containment: "parent"`
- `scroll: false`

The current `zIndex` option seems fishy.

Is the `dragAndDrop` option necessary?