Changed Content-type

Response is always in JSON... so why not change Content-type to JSON?
Merge branch 'devel' of github.com:LAndreas/phpDNSAdmin into devel
Added ability to parse json objects sent in http payload if content-type in request is set to e.g application/json
Fixed intents.
Merge pull request #4 from LAndreas/devel

Changed Content-type & added ability to parse json objects in http payload