Fix JavaScript error when using TagsInputWidget

When using a `TagsInputField` in a form and `TAGS_INPUT_INCLUDE_JQUERY` is enabled, Chome on OS X throws this JavaScript error:

    Uncaught TypeError: Object [object Object] has no method 'tagsInput'

It's because the tagsinput plugin's script is loaded before jQuery itself is. Tweaking the `TagsInputWidget` class to make sure the plugin is loaded after jQuery fixes the issue.