Add col-sm-* to catalog/show.html

So it's still two-column at size bootstrap 'sm'. catalog/index
was changed to still be two-column at 'sm' here: 8a51ec61fc02

Should catalog/show be changed to match? If so, this does it.
Merge pull request #975 from projectblacklight/catalog_show_col_sm

Add col-sm-* to catalog/show.html