added ability for manager to change users role

* AR enums suck, looks like a hash but not a hash
* created form for user and form for manager
* different params for user vs manager as well
Yeah this could get tricky because `Location` is an association and all those methods are provided by Rails itself. There are a couple of [SO suggestions](http://stackoverflow.com/questions/17127358/implementing-a-nullobject-pattern-in-rails) for overriding the built-in methods and providing the null object, but I am not too thrilled with that prospect. I'd probably prefer the `allow_nil` option at this point, but it'd be interesting to get Eric's take at some point.