User profile settings form

* Add User model form
* Add `settings.html` template using the form
* Add `privacy_controls.html` partial (which will also be used in popup from profile page)
* Add views
* Strip whitespace from first/last name in `User.clean`

In a future PR:
* Add Bootstrap so tab panels will work
* Add JS to enable/disable privacy controls and set hidden fields
I'm still not sure I agree stylistically with doing the `render_to_response` in the view function rather than as a wrapper.

That said, if you're going to, consider returning a dict and explicitly wrapping this function like so:
```python
@render_template('users/profile.html')
def _render_user_profile(...):
    ...
```
This ensure we create the template context in a consistent way, and prevents having to type out ` context, RequestContext(request))` all the time.

And consider doing something similar for the other view functions here.