Redesign

This pull request tracks work on a redesign of the header, sidebar, and main page map based on the presentation ([video](https://vimeo.com/mapbox/review/75978159/984cfdb5af), [slides](http://jfire.io/sotm13/), [mock ups](https://github.com/samanpwbb/osm-redesign/tree/sotm-birmingham/renders)) at State of the Map Birmingham.

Major components of the redesign include a new help page; new about page; moving navigation elements out of the sidebar; moving search results, export controls, changeset history, and feature details into the sidebar; and removal of the sidebar from "interior" pages such as the user profile and diaries.

**[Test Deploy](http://redesign.apis.dev.openstreetmap.org/)**

## TODO List

* [x] Design and implement about page
* [x] Style sign up / log in
* [x] Move edit button to 2nd position
* [x] Clickable logo/project name
* [x] Content width for interior pages
* [x] Add call to action button to main sidebar
* [x] Implement closing the sidebar
* [x] Hook up interactivity for changeset view (load changesets for current view, update on map move)
* [x] pushState-based navigation
* [x] Restore "Where am I?"
* [x] Include object in "Edit" links on browse pages
* [x] Active states for all nav elements
* [x] "Where am I?" needs to have own route
* [x] Integrate/combine "Map Data" layer and browse pages
* [x] Implement responsive design for header
* [x] Reduce "Where am I?" lat/lon to 7 digits precision
* [x] Fix map controls on user settings page
* [x] Test FF, IE, RTL