Update plugin options to allow navigation to take more/all available options

[paulrobertlloyd]

The service navigation component has a number of options that enable various text strings and features to be configured, such as the table used for the menu button and the ability to include a service name in the navigation.

While the plugin, as of v6.5.0 uses the service navigation component, it maintains the options that were previously used for the X-GOVUK primary navigation component, which are quite different. (See #316)

In the next breaking release, there’s an opportunity to update the plugin options we support for navigation (or maybe replace with service?) to enable more complex navigation to be used.