Fixes #663 - adds phone helper for results

Fixes #663 - adds phone helper for search results so that the first
voice or hotline phone number is displayed on the search results list,
or none if either no number or only numbers of type `tty` or `fax` are
found. Also, singularizes HTML class from `phones` to `phone` for
search result entries and removes unneeded list for phones.
Using the `#select` method from Ruby's [Enumerable](http://ruby-doc.org/core-2.1.4/Enumerable.html) module, you can simplify the method into one line. Given an array of phones, you want to select the first one that is either `voice` or `hotline`. If you break it down into small steps, first you want to look inside the array and keep only the phones that are either voice or hotline, then you want to pick the first item in that new array. You can combine both of those actions by chaining them, like this:
```ruby
phones.select { |phone| phone.number_type == 'voice' || phone.number_type == 'hotline' }.first
```

To keep the line length under 80 chars, you can do this:
```ruby
phones.select do |phone|
  phone.number_type == 'voice' || phone.number_type == 'hotline'
end.first
```
But chaining with `do..end` looks ugly, and is not recommended by the [Ruby Style Guide](https://github.com/bbatsov/ruby-style-guide#single-line-blocks). Instead, break everything up into small methods: one method that determines if a phone is a voice or hotline, one that selects all phones that are either voice or hotline, and one that picks the first one from the previous method. Or you combine the last two actions into one, something like this:
```ruby
phones.select { |phone| voice_or_hotline?(phone) }.first
```
This makes things more flexible in case you wanted to make sure that a voice number was always returned. For example, if both a hotline and voice were present, and the hotline was listed first, the hotline would be returned in your original implementation. If you wanted to always make sure the voice number was picked, you could add another method that sorts the array by number_type and picks the last one.
```ruby
phones.sort_by { |phone| phone.number_type }.last
```

Finally, I would put this in its own helper module in a separate file to keep all phones-related methods together.