docs(tutorial): display button icons (Previous, Live Demo, ...)

Request Type: docs

How to reproduce: For example, see http://docs.angularjs.org/tutorial/step_00

Component(s): 

Impact: small

Complexity: small

This issue is related to: 

**Detailed Description:**



**Other Comments:**

In relation to https://github.com/angular/dgeni-packages/pull/8

The icons are not visible yet, this commit do the necessary.