Swap out OSD viewer for thumb when loading errors out.

Begins work on #118 (leaving open for know to discuss alternate approaches that would require changes to the stacks IIIF service).

#### Example SU Only object (bd117rc5047)
![bd117rc5047-static-thumb](https://cloud.githubusercontent.com/assets/96776/5055703/e172eae8-6c1c-11e4-80db-28c7641724ae.png)

#### Example read=none object (bb066bf1599)
![bb066bf1599-static-thumb](https://cloud.githubusercontent.com/assets/96776/5055714/15230ae4-6c1d-11e4-9658-7060c0c5be52.png)