Add minimal version with centered layout and padding wrapper

Thanks for the boilerplate Sean. After building several emails, I have trimmed things down to a minimal starting point that I find most useful. 

The version I added has centered content area, an edge wrapper to control padding, and a page wrapper to control the body background. 

The head styles are grouped into "reset" and "bring inline", and include only those that I have found to be effective at avoiding recurring bugs. 

The media queries have been removed, since they are not special or unique for emails. The Outlook query was left in place because that client tends to break in unique ways.