forced ie7 into single column view to avoid need for box-sizing polyfill

@triblondon 

I'm thinking of maybe removing the following too as they encourage non-responsive products:

* `$o-grid-fixed-layout-selector: null !default` overrides choice of useragents (normally ie8) with a custom selector
* `$o-grid-is-fixed-desktop`: \[false\] Forces the site to always use the large layout
Also mention of ie7 & <ie9 in the comment looks like it could be a mistake. How about

> Styles to be hidden from IE7/8 
> We need to set a minimum width because @media screen works in IE7/8