Geocoding

[Pivotal Tracker](https://www.pivotaltracker.com/story/show/66038900)
* Added [geocode](https://github.com/alexreisner/geocoder)-gem
* Added scenarios to `user_list.feature` and to `profile.feature`
* Added spect to modal spec for User
* Updated views for `user/index` and `user/show`

* Moved login and Sign-up links to header