Users can search dive sites

https://trello.com/c/BSCAV8cq/36-users-can-search-dive-sites

![searchdives](https://cloud.githubusercontent.com/assets/8681076/5304160/fa144730-7bbd-11e4-8f0b-f538b7109517.gif)

Overall I still don't like the idea of falling back to all when the search yields nothing. The code is confusing, and the UI is as well. To me it's much clearer to just show an empty results set and message saying "no matches found" and let the user clear the search or search again.

That said, if you decide to continue with that, I would like to see the code closer to:

``` ruby
@dive_sites = search_results_or_all
```

then that method is

``` ruby
def search_results_or_all
  search_results = DiveSite.search(params[:search])
  if params[:search].present? && search_results.present?
    search_results
  else
    DiveSite.all
  end
end
```