ref #339 -- TimberMenu should match wp_nav_menu behavior of falling-back to wp_page_menu
ref #339 -- added test to verify normal menus worked and weren't taken over by default page menus
ref #339 added additional test to verify that passing a non-existent menu value does NOT return the pages menu
Merge pull request #353 from jarednova/339_pages_menu

ref #339 -- TimberMenu should match wp_nav_menu behavior of falling-back...