Restaurant creation

Creates a restaurant and does basic server-side validation checking for non-null string and if you already have a restaurant.

Also display messages and create session header.  Currently, these partials must be manually added to the html templates.
Another ruby style thing: leave off the `return` when it's the last statement in the block. Also use your comparison helpers. This line should likely read:

``` ruby
def has_restaurant?
  restaurant.nil?
end
```