Consider alternatives to regexing HTML

[austinpray]

• sage/lib/nav.php

  Line 47 in a179515

  $item_html = preg_replace('/<a[^>]*>.*?<\/a>/iU', '', $item_html);

• sage/lib/nav.php

  Line 49 in a179515

  $item_html = preg_replace('/<a[^>]*>(.*)<\/a>/iU', '$1', $item_html);

This is definitely pretty brittle. We should be using https://php.net/manual/en/book.dom.php here. Although I don't know enough about the community at large to know if this will cause problems for people. PHP Dom module is always enabled by default right? Need feedback.

[retlehs]

irrelevant if #1427 is merged.