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)
More questions about presenters: user_presenter.rb has a `display_name` method. This method, and its attendant `full_name` and `email_designator` methods are defined in the model, but deal exclusively with presentation. Plus, `display_name` is tested in user_presenter_spec.rb, and the other two appear to not be tested at all. Is this intentional or work in progress?