Add option to show total query execution count and time without rendering the full query log

For whatever reason on very slow page loads sometimes the query log box will fail to be displayed, however commenting out $output .= devel_shutdown_query($queries); in devel_shutdown_real() allows the summary line (with total query count, total query time, page execution time, memory usage, etc.) to appear, without having to render the full query log table.

It can be useful to know total count and query time to debug performance issues, without needing to drill down into the individual query data, hence why having the option to show only this top level information would be a useful.