Feature: contest admin overview

## Ready State: Yes|No

This pull request is related to the following JIRA tickets:
https://imagex.atlassian.net/browse/LDC-255

Finalist & winner fields have been refactored so the contest entry nodes store that data not the contest nodes. Fitted better with default Drupal functionality.

## Requirements & Dependencies

None

## Deployment Instructions

* Merge code.
* Enable module imagex_contest & imagex_contest_permissions
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

* Create a contest node
* After creation, on contest node view, click the "Submit your entry now" link and submit a new contest entry node
* Go back to the contest nodes and ensure:
  * You see a new "Contest Overview" tab when logged in as admin
  * The "Contest Overview" lists all submissions for the given contest
  * Submissions can be deleted, selected as finalists or winners in bulk