Display concurrent refs as a multiline shield

This builds upon #745, but although I consider that ready to merge, the changes here need more review.

This PR changes how multiline refs are rendered. Instead of a long string split with ``;``, it displays each ref on its own line, as part of a taller but narrower shield.

By going to 11 characters wide, 99.2% of refs (by split numbers) will be rendered and with 4 high 99.99% will be rendered.

Some examples

![image](https://cloud.githubusercontent.com/assets/1190866/3639702/0e295b28-1086-11e4-9e4f-243ca0c008aa.png)
![image](https://cloud.githubusercontent.com/assets/1190866/3639709/2e565a54-1086-11e4-9d9d-ff5ad4ba03b8.png)
![image](https://cloud.githubusercontent.com/assets/1190866/3639738/7db70f70-1087-11e4-8cb9-610fabf400fc.png)
![image](https://cloud.githubusercontent.com/assets/1190866/3639744/9d3a3f34-1087-11e4-8367-54baccaf4dcf.png)

Issues

* Cross-MT shield rendering errors are more obvious. I could only find one with 2x2 metatiles and a 128 buffer, so the previous work to reduce the frequency has made them more common, but they're pretty obvious when they do happen. I couldn't find any at 256 buffer.

* Shields with one wide ref and two or three narrow ones look imbalanced.

* Spaces aren't removed from the outside of each ref line. I'm inclined to leave this, to push data consistency. 

Overall I like the changes, and I think they set us up stylistically to tackle #596