File input is incorrectly wrapped in a border box

## Problem
File input is incorrectly wrapped in a border box:
![screen shot 2014-11-12 at 10 57 34 am](https://cloud.githubusercontent.com/assets/3778206/5014449/7962fe2e-6a5b-11e4-9baf-ec8e638c9061.png)

## Solution
Exclude the `form-control` css class from file input elements:
![screen shot 2014-11-12 at 11 00 57 am](https://cloud.githubusercontent.com/assets/3778206/5014451/7c509024-6a5b-11e4-9bc0-d60113c6349e.png)

- also slightly modified the input example in the docs to display labels and show an example of input of type email

## Testing
- CI tests pass (unit test added for this case)
- verify that input of type file appears as expected (screenshot above can be seen in the docs in this branch)