Retry submitting results

[madduck]

If a result fails to submit, currently the app crashes. When a match result cannot be submitted to the PostResult-URL, then the software should please keep track of that and retry a few seconds later, until success. Else I cannot rely on the software to actually provide me with results, since Wifi might be overloaded, or some other cosmic radiation problem could cause the app to fail to submit a result, thus effectively losing it. I know it's not lost, but as tournament control, I would need to (a) first determine that a result has not been uploaded, and then (b) find the tablet to upload the result manually, which may be a real problem if the next match has already started.