CORE: social media field for addthis

## Ready State: Yes

This pull request is related to the following JIRA tickets: [IXB-1: Sample Ticket A](http://imagexmedia.com).

## Requirements & Dependencies

* features, imagex_addthis

## Deployment Instructions

* Merge code, enable imagex_addthis

## Usage/Test Instructions

* confirm add this field has been added to blog content type