Retry several times when there's a connection error

[Dremora]

Sometimes MusicBrainz returns (or at least, it did before NGS) an error, especially during multiple queries. In this case, user has to start over (and still may encounter the same error again, which happened to me repeatedly). This is probably related to the “1 query per second” rule, which is currently not obeyed, but still:

1. If the error is encountered, wait several hundred miliseconds and try again
2. In case of continuous errors, drop after 5(?) unsuccessful requests.