User timezone

Pivotal story "Calculate and display timezone": https://www.pivotaltracker.com/story/show/66286674

- Using 'nearest_timezone' gem to determine user timezone based on lat/long coordinates, without any external calls. 
- Added a `describe 'geolocation'` block to spec/views/users/show.html.erb_spec.rb, grouping tests for the implemented timezone display with two new tests for user country display.

![image](https://cloud.githubusercontent.com/assets/5029403/3790668/1378d06c-1b13-11e4-8b1d-023f9695245d.png)
@sampritipanda Thank you for giving me impetus to learn about presenters! Regarding their implementation on WSO: if their purpose is to remove logic and presentation detail from views, would it not make more sense to replace in _summary.html.erb e.g.
```HTML+ERB
<% if presenter.country? %>
  <li><i class="fa fa-globe fa-lg"></i> <%= presenter.country %></li>
<% end %>
```
with
```HTML+ERB
<%= presenter.country %>
```
and in user_presenter.rb have
```ruby
def country
  if user.country?
    content_tag(:li, ...)
  end
end
```