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
Consider making this visible and removing the text.  For OTM2, we used "visible" checkboxes wrapped in a `<label> that were hidden via [CSS](https://github.com/OpenTreeMap/OTM2/blob/master/opentreemap/treemap/css/sass/modules/_checkboxes.scss) for our "fancy" checkboxes.

I imagine we might do something similar here.