Unplugged activity updates


- Support new lesson plans, pairs of links to html and pdf documents
- Show lesson plan html in an iframe
- Move videos to use specified keys rather than assumed the same as unplugged level key
- Add first course's unplugged levels
- Hide lesson plan for logged-in students

# New lesson plans: student vs non-student

![image](https://cloud.githubusercontent.com/assets/206973/3590883/e5ce504c-0c5d-11e4-9a87-85a92975a4d1.png)

# Old lesson plans: student vs non-student

![image](https://cloud.githubusercontent.com/assets/206973/3590893/fd63b7c4-0c5d-11e4-9d07-79e35adbb14e.png)