Adds basic image viewer (single image)

* Displays single image view (first image if object has multiple images) using OpenSeadragon
* IIIF info.json AJAX call works only with `https://`, and hence new `iiif_stacks_url` in settings file
* Fixed/updated common styles and formatting

![image](https://cloud.githubusercontent.com/assets/302258/4611108/fffca082-52b6-11e4-9e4f-a8e09999cfd1.png)

is this intended to be opened in new tab?