Navigation updates

This PR updates the navigation to integrate with the latest templates.

TODO:

- [x] Remove the "active" property which is no longer required
- [x] Add `jsonSerialize` support to `NavigationItem` now that tickit only supports PHP 5.4+
- [x] Integrate the latest navigation with the navigation list response
- [x] Add new navigation type for the settings drop down
- [x] Add "icon" support to `NavigationItem` which will dictate client-side appearance
- [x] Add click event handling for navigation items
- [x] Add support for the "Create Ticket" button which displays slightly differently
- [x] Move names of the navigations to `NavigationBuilder` as constants