Use responsive col-sm-4 on homepage

[altheadotspace]

Bootstrap's col-xs-* classes are always rendered horizontally - the stats and issues columns were causing smartphone-sized displays to break the rest of the layout:

I switched them to col-sm , which stacks them vertically for "xs"-sized devices and goes back to horizontal for larger ones.

I used http://getbootstrap.com/css/#grid-options for reference.

[dlapiduz]

Thanks @zekeweeks!! I was meaning to do something like that...