Feature: LDC-251 & LDC-252, LDC-258 - contest & contest entry displays

## Ready State: Yes

This pull request is related to the following JIRA tickets:
* https://imagex.atlassian.net/browse/LDC-251
* https://imagex.atlassian.net/browse/LDC-252 (addThis) (roll into this PR as need to change panelizer settings)
* https://imagex.atlassian.net/browse/LDC-258

All related to contest & contest entry displays so bundle together to reduce potential conflicts.

Contest nodes use panelizer to allow admins adjust displays based on whether the contest is open to entries/voting or has finished. Default pane visibility settings mean the default layout should be sufficient in most cases.

Contest Entry nodes use the default node view but have classes injected if they are selected as finalists or winners to allow some variation in the theming:
* node-contest-entry-finalist 
* node-contest-entry-winner

## Requirements & Dependencies

imagex_addthis hotfix https://github.com/imagex/imagex_addthis/pull/3

## Deployment Instructions

* Merge code.
* Enable imagex_contest & imagex_contest_permissions & imagex_contest_addthis
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

### LDC-251 & LDC-252
* Create a contest node and ensure:
  * Default panelizer layout is shown
  * Selecting an entry as a winner or finalist (via node/NID/contest) makes them show on the contest node view
  * Closing entries hides the "Entries Deadline" from display
  * Closing voting hides the "Voting Deadline" from display
  * AddThis button is shown
* Create a contest entry node and ensure:  
  * When selected as a finalist or winner that additional classes (node-contest-entry-finalist, node-contest-entry-winner) are added to the wrapper div.node
  * AddThis button is shown 

### LDC-258

* Create some test contest nodes with different "Open For Entries" & "Open For Voting" settings
* Create a new page node and then use panelizer to add a new views pane "Imagex Contest Contests: Contests Content pane" (Under the ImageX category) and ensure:
  * You can hide certain fields using the "Fields to display" settings
  * You can alter the number of items shown & choose to use a pager or not
  * You can filter the contests by "Contest Open For Entries?" and/or "Contest Open For Voting?" (can be useful for creating different blocks depending on the "phase" of the contest
  * You can order contests by post date, entries deadline or voting deadline

#### NOTES

* I simplified this to hit the deadline
* Voting functionality will be covered in https://imagex.atlassian.net/browse/LDC-259
* In testing I noticed the imagex_addthis module was missing the addthis_displays module as a dependency which basically means nothing is rendered in the addThis fields (across all content types), made a hotfix for imagex_addthis https://github.com/imagex/imagex_addthis/pull/3