Add merged image collection behaviors

Closes #198 

**Note:** The merged image collections can only be identified on an item merge solr index.  We could add some logic about trying to map them, but it looks like we may be launching item merge to production next week anyway.

### Search result
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![meged-image-collection-result](https://cloud.githubusercontent.com/assets/96776/3137535/f76709a6-e855-11e3-9ed5-998198384ae5.png)

### Record view
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![merged-image-collection-record](https://cloud.githubusercontent.com/assets/96776/3137536/007837f4-e856-11e3-852b-04fb9b22e533.png)