Make Automation REST API compatible with OAuth and OpenSocial call

OAuth implies that POST requests must be x-www-form-urlencoded
=> need to adapt OAuth filter to handle POST request
=> need to update Automation Server so that we have a compliant MessageReader

Furthermore Automation uses some additional headers to configure the output.
OpenSocial does remove all the header except the OAuth headers.
Even if we can fix this in Nuxeo/Shindig implementation, this will still be an issue for almost all OpenSocial containers.
=> must provide an alternate solution based on the POST body content