4th set of column classes

Created by: rpedela

Currently there are 3 sets of column classes, but 4 default screen sizes as specified here. Specifically col-lg-* has a double meaning. It is for screen sizes of 992-1200 and 1200+. I would like to see this broken up so that there is one set of column classes for 992-1200 and another separate set of column classes for 1200+.

The reason is that some content on the website I am building needs different column settings for medium and large devices.