Create Search Functionality

Create search results control
Update listings model with search methods
Create search form partial
Create search results partial
Add search and home links to application
Create search results show page
I wouldn't make this abstraction unless you needed it in fact, for now I'd do the following:

```ruby
def self.search(search_params)
  if search_params[:city].present?
    city(search_params[:city])
  else
    all
  end
end
```

Then just wait until you have more search problems to solve to decide how to abstract.