api response content_type should be application/json

Our server requires the http_accept header with our custom api mime type but the response content_type header should be application/json and understandable to any client.
return json response for missing routes
Revert "api response content_type should be application/json"

This reverts commit 8f3a76304bc6efd72effa9ba0f4018453be46819.

JSON API response should reflect the requested HTTP_ACCEPT header.
use normal JSON content types for non-API routes
remove duplicate RecordNotFound rescue
allow ProjectSerializer to gracefully handle empty project_contents association
Merge pull request #99 from camallen/nil_project_contents

allow ProjectSerializer to gracefully handle empty project_contents
Merge branch 'fix_api_reponse' from pull request #91
Move user session and password management out of api
Make sure devise controllers respond with both html and json
Fix sign in order
Add json sign and sign out methods
Allow resource owner credentials with devise session
Regenerate CSRF tokens on log-in log-out
Add specs for devise login
Return list of auth providers when requesting /users/news as json