Add iD editor

iD sources live in vendor/assets/iD, and are managed with
vendorer, using the "rewrite" functionality to replace relative
paths in the CSS with <%= asset_path(…) %> directives.

To avoid needing to namespace all of its CSS classes, iD
is embedded via an iframe.

To setup, edit application.yml to include an `id_key` key.
(It can use the same consumer key as P2 if you like.)
Update iD; clean up OAuth configuration
Fix edit links on browse and changeset pages
Call updatelinks when map moves

Fixes systemed/iD#1330.
Fix search results display (systemed/iD#1328)
Load search result locations in iD
Update iD
Support maximize/minimize (systemed/iD#1327)
Fix search result link behavior (systemed/iD#1329)
Selecting relations is now supported
Update iD, set locale
Show object icons in the margin on data browers pages

Avoids indenting the text which looks odd, especially for things
which don't have an icon.
Show icons in browse history views
Fix browse view display issues in medium width windows

Floats are evil - using inline-block instead makes the whole thing
easier and more stable.
Show node coordinates in the right place
Append "view details" link to Nominatim search results
Style the "view details" link in search results
Replace some inline javascript with a UJS solution
Update to iD 1.0.0
Switch to stable branch