Demos: Filterable: Re-worked to reflect the current state of the widget. Fixes #6227, #6229, #6230, #6231.
Filterable backcompat: Prevent default on generated form submit and blur input. Fixes #6226.

See 336db34e031b0815c807554796519cd34d28c153 and #3303.
Navigation: Do not submit forms via AJAX if the "submit" event default is already prevented.