Replace Object.assign for IE support

Calling this[fn].bind requires extra check

Removed brackets in typeof

Calling this[fn].bind requires extra check - cont.

Checking `typeof(this[fn])` is enough

trigger most specialized events first

new PR for https://github.com/RubaXa/Sortable/pull/741

small fix with #373

React Mixin - Fixing check for existence of getDOMNode function

knockout-sortable - prioritise global dependencies if available

Throw error if call in node

Allow event functions to be defined as functions AND strings.

The current behavior (in `master`) is to define the handling functions for events as strings. Default for `onSort` for example is `handleSort`. Commit 8cef762d changed this behavior forcing handling functions to be defined as functions in the options. This breaks all existing code, resulting in a no-op even with the default options (which still define the default handlers as strings).

This commit restores previous behavior AND allows you to define your handlers as functions directly, if you’re so inclined.

#666 Return DOM information of element in env object

`scope` does not has "off" function