Add Filter: bu_navigation_format_page() for Args

[acketon]

There is a filter in bu_navigation_format_page() for the HTML of a page link in the nav, but no filter to adjust the arguments of that function. It would be nice to be able to do so in order to easily add a class to a page item, or adjust the title_before or title_after properties and still make use of that function to generate the HTML for the nav link, li, etc.