Add OpenSeadragon viewer for stacks images

Closes #245 

Adds image viewer to both image and merged image record views.

A few outstanding issues that will need to be addressed upstream:
1. Fullscreen view for multi-image does not display the fill image width (screenshot below).
2. Previous/Next pagination of images does not work. Requires upstream hooks.

### Single Image (unmerged)
---
![unmerged-image](https://cloud.githubusercontent.com/assets/96776/3223777/cae32bc4-f027-11e3-8f64-c66e4a4ec4f5.png)

### Multi Image (merged)
---
![merged-multi-image](https://cloud.githubusercontent.com/assets/96776/3223779/d59212ec-f027-11e3-94aa-8f0785613db2.png)

### Multi Image Fullscreen Issue
---
![multi-fullscreen](https://cloud.githubusercontent.com/assets/96776/3223782/df4a4bf6-f027-11e3-8bbc-6de1c6f14bd9.png)