schema is not hardcoded into client anymore
api: moved all the experiments to an own file
refactored error handling

* use connect-style callbacks for error handling
* api endpoints returns error in JSON format
implemented sources api endpoint
implemented overview of sources
wrote an example document of data sources
fixed a bug for deletion of a source
client: ability to delete sources
client: ability to create new ressources
api: minor bug fixes
api: delayed the responses (for a more realistic load time)
ability to edit sources