Perform a generic GET-request to a target server, storing the received data in a variable.
- The device needs to be connected to the internet.
- getURL: url of the server to send the request to
- getGroup: group to store the result in
- getKey: key to store the result as
- On success: The request has been performed successfully, the server answered with 'ok'.
- On fail: The request has been performed successfully, the server answered with 'error'.
- On missing url: No target url has been provided.