Register test

Close #6 and #10 
response for success:
````
{
  "success": true
}
````
response for invalid json:
````
{
  "success": false,
  "error": {
    "message": "POST data could not be decoded. Please make sure json is valid."
  }
}
````
response for missing Magento secret keys:
````
{
  "success": false,
  "error": {
    "message": "Missing Magento url secret keys."
  }
}
````