UP-4069 : fixed issue with medium sized screen not resizing correctly

In respondr.xsl we are using col-md for the middle column, so this changes the side columns to use these as well.  Also does this for precontent region.

## Before: 

![image](https://cloud.githubusercontent.com/assets/3534544/2769261/f92b2792-ca4e-11e3-9ad0-232267c11485.png)


## After 

![image](https://cloud.githubusercontent.com/assets/3534544/2769257/f098182e-ca4e-11e3-8ced-b7a42e12c119.png)