Port filter styles from Transition app

Bring across white filter styles from Transition. These should
eventually live in the admin template.

* Introduce a nag-compact style which has less padding
* Highlight active filters
* Introduce a remove filter button
* Reduce size of chevron in filter
* Add ‘pill’ styles for text only items in a nav-pill container
Add a 'remove all filters' link

Quickly return to the original list of users