Minor cleanup.

I have a few minor edits here that you might want.

Had some warning messages popping up when WP_DEBUG=TRUE, got rid of those. One was about $active not being declared, and others in the menu_walker class about non-objects in $args.

The navbar was hidden behind the WP admin bar when logged in, added some CSS to fix that.

Also put in a wrapper on the 'Primary Menu' creation that checks for an existing menu called 'primary'. This way child themes can rename that menu, even if they can't change the slug.