Get indexOf interactables when splicing
Update element classnames when changing options
Use indexOfElement to get index using element

No longer override protype indexOf with method to find index using
element.

Also fixed Interactable#isSet
Use actionable option properties when setting

The options object passed to interact.set should have properties
'draggable', 'resizeable' and gestureable set to true to enable each of
the related actions (no longer 'drag', 'resize' and 'gesture').
Update demo
Update tests