Replace icon fields with dropdown

Fixes #2365. Replaces the icons for a dropdown as the icons are not intuitive enough and hard to expand when we have more fields to add (we would have to commission additional icons from the great maki artist).

Before:
![screen shot 2014-10-30 at 4 15 42 pm](https://cloud.githubusercontent.com/assets/58878/4851509/d9ed7488-6072-11e4-96a0-99f13ed3e615.png)

After:
![screen shot 2014-10-30 at 4 16 17 pm](https://cloud.githubusercontent.com/assets/58878/4851508/d9e92090-6072-11e4-9aa5-a7b288c459be.png)

@jfirebaugh mind reviewing?