Close #4760 - .json requester should return a header Content-Type: application/json, .jsonp application/javascript
Close #4760 - .json requester should return a header Content-Type: application/json, .jsonp application/javascript

 * set good values for headers
 * testplatform not fullscreen still working with IE (use __content_type=text/plain)

Former-commit-id: 0320bd5ae72161a83ba4ac15198ad16d0bcc37da
Former-commit-id: 7d879bea054c375418ff3f55ae2cb53bc3df0427
Former-commit-id: 02b86b4d7c773d28ff00800fd945f133d41bba0f
Former-commit-id: c5560370a1d214cca314fedb10497c93a497c0e3
convertigo/convertigo-webapp,convertigo/convertigo-webapp