Autoscroll while dragging

[uniring]

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.

New available options are:

* scroll                  (false)   Enable or disable the scrolling behaviour
* scrollSensitivity       (1)       Mouse movement needed to trigger the scroll
* scrollSpeed             (5)       Speed of the scroll
* scrollTriggers          (obj)     Distance from the border where scrolling become active
    top: 40
    left: 40
    right: -40
    bottom: -40

Solves Issue #17

[RamonDonnell]

Thanks for this. It is worth mentioning this adds jQueryUI as a dependency to the project.

[TomNM]

Something needs to scroll, even the browser window, when you're dragging.

[peters]

/cc @dbushell This one as well. Works as expected with and without jquery ui.

[nagarajhubli]

It's not working for me unless I include jQuery UI (draggable module and the corresponding depencies), also any help in making it work for IE8 will be appreciated