[ticket/10472] Fix ACP overflow:hidden problem for medium-sized screens

https://tracker.phpbb.com/browse/PHPBB3-10472

Hope to fix a long standing problem. Certain tables in the ACP are particularly wide (like add/edit smilies), and with an `overflow: hidden` rule they are simply not visible at all.

By reducing the width of some of the worst offenders (`input[type="number"]`) in particular, and having proper clearing rules, we can show these tables, even though they break out of the container.

I know its not ideal, but having some horizontal scrolling outside of the container is significantly better than not being able to see certain settings at all.

PHPBB3-10472