Define $element.data('bs.tokenfield') earlier.

Define `$element.data('bs.tokenfield')` at the beginning of `Tokenfield()` instead of after initialization so the Tokenfield object is also available through `$(this).data('bs.tokenfield')` in events triggered during initialization. This is useful when `tokenfield:createtoken` or `tokenfield:createdtoken` events have been attached before initialization, so they are run on page load if the tokenfield input has a default value on page load.

Before this fix you would get an error if you tried to use `$(this).data('bs.tokenfield').$input` inside a `tokenfield:createtoken` event that was bound before tokenfield initialization like this
```javascript
$('#tokenfield')
    .on('tokenfield:createtoken', function(){
        var $input = $(this).data('bs.tokenfield').$input;
        // Do something with $input
    })
    .tokenfield()
```

You could just bind the event after `.tokenfield()` but then the create event would not be run on initialization (on page load)  when tokens are created from the default value attribute of the `#tokenfield` input.

Before this fix you could use a workaround of recreating the tokens after initialization to fire the create events like so `$('#tokenfield').tokenfield('setTokens', $('#tokenfield').tokenfield('getTokens'));` but this is not needed anymore after this commit.