Implement primitive functional cond blocks.

![screen shot 2014-11-26 at 3 07 34 pm](https://cloud.githubusercontent.com/assets/8001765/5210395/998300d4-7580-11e4-887c-bb0af656b55f.png)

![screen shot 2014-11-26 at 3 09 09 pm](https://cloud.githubusercontent.com/assets/8001765/5210398/9d178eb8-7580-11e4-9eaa-d442090f94e0.png)


I personally don't like using variable name to indicate that it's optional. We have this a bunch in blockly-core, but would prefer to keep it out of blockly. Instead just call it wrapWidth, and potentially set it to a default value in the first few lines of the function if it's undefined.