Added user information to determine if they are logged in

[migurski]

On ODES pages, user_id and user_nickname template variables determine whether a user is authenticated. @binx handing this over to you for UI.

• [x] Showed logout button on ODES pages with user's nickname
• [x] Make the logout form look like it belongs with the styleguide.
• [x] Link to existing extracts page on the index if user is logged in

Closes #114.

[binx]

[binx]

@migurski can we add login information on the index page too?

[migurski]

Back to you; give it a try via https://mapzen-odes-extracts-pr-122.herokuapp.com/oauth/hello

[binx]

@migurski what do you think of this?

[migurski]

LGTM.