add folded line icon

Simple tweak now that the Gutter API landed!

Screenshot:
![image](https://cloud.githubusercontent.com/assets/253202/3225392/a4b2f92a-f04f-11e3-8ab3-51cfc999641a.png)


This condition needs to be in there for class application. Looks like `isSoftWrapped` is a bool, not a fn.