Feature: LDC-311 - part of aggregator dashboard integration

## Ready State: Yes

Contains half the work involved in this jira task: https://imagex.atlassian.net/browse/LDC-311

## Requirements & Dependencies

None

## Deployment Instructions

* Merge code.
* Enable module `imagex_aggregator`
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

* Go to /admin/content and ensure you can see a new "Imported Content" tab within secondary navigation
* On the "Imported Content" page ensure you can edit/delete/publish/unpublish imported content in bulk