Lea add locations prices to posts

Added a dropdown to the new post form, from which users can choose their location.
Added a field for entering the posted item's price to the new post form.
Wrapped the new post form in a signed-in? conditional, so only signed-in users see the form.
I originally had the "form.", but it causes rails to attempt an unnecessary merge, leading to this error: 

undefined method `merge' for :location:Symbol

Here's where I figured out how to fix it:
http://stackoverflow.com/questions/8147069/collection-select-method-gives-error-in-rails-3-1-1