Core:  Initial commit of imagex_group content type

## Ready State: (Yes|No)

This pull request is related to the following JIRA tickets: https://imagex.atlassian.net/browse/LDC-74

## Requirements & Dependencies

* This module requires radioactivity, and feature modules
* linux_group is dependent on this module.

## Deployment Instructions

* Merge code.

## Usage/Test Instructions

* ensure after install that imagex_group is enabled in features and imagex_group content type has been created.