Add prefix field to a profile node type.

#5744 

As mentioned in the issue above, a field named "prefix" is added to a profile.
Node form for a profile:
![selection_245](https://cloud.githubusercontent.com/assets/4497748/3226250/53570a98-f069-11e3-9921-351792a35d86.png)

The ``john/people`` page:
![selection_238](https://cloud.githubusercontent.com/assets/4497748/3214157/b2c4f600-efa8-11e3-8463-c5e2104da2e4.png)