[ticket/12704] Improve the load time information in the footer when enabled

PR #2570 has added new constant to display load time information without
debug mode is being on (https://tracker.phpbb.com/browse/PHPBB3-12687).
This patch expands the total load time info with SQL/PHP load times,
while hiding the additional info with <abbr> element.

<a href="https://tracker.phpbb.com/browse/PHPBB3-12704">PHPBB3-12704</a>.