Item mqs

A little refactor for the media queries (sorry medium queries) on the items.

`fc-item--standard` and `fc-item--list-media` are used on both desktop and mobile but always came with queries for either mobile or desktop. This moves those specific media queries into `_items.scss` where the original media query is made.

tl;dr – We were duplicating media queries by having them inside media queries. Now we don't.
should this be nested under `tablet`? ends up with `(min-width: 61.25em) and (min-width: 46.25em)`