Autoscroll when dragging

Autoscrolls the container element while dragging if you drag the
element over the offsets defined in scrollTriggers config option.

Also you can enable/disable this behaviour (disabled by default to be
backwards compatible) and control the scroll sensitivity and speed.
Add "toArray" function

Designed to work seamlessly with the nested set model
Merge branch 'pr/46'
Merge branch 'pr/73'