Ember route 404

7653c87 [#82675948] move chosen-sprite.png so it is precompile'd …
This stops the 404 when a user tries to add contributors
on staging or production.

7653c87 [#82675948] ember catch-all route will only respond_html …
This makes it easier to find bugs for URLs that do not exist.
At least for formats other HTML they will cause Rails to serve
500 errors.

https://www.pivotaltracker.com/story/show/82675948

— DT