Add underscore (back) and underscore.string
Use button instead of anchor tags

* Changed use of anchor tags for button tags as they have a preferred
semantic meaning in this context. The Add buttons are just that, buttons
and should be represented as such.
* Work in progress on the first card block rendering. Data set items now
show but need to add the Add buttons.
Hoooooooooooah! First example is generated dynamically now

Onwards to the second and third examples! Hooorah!