Use CoreUtils::redirect instead of header(...)

There's a few left
grep shows:

```
[lordaro@urybsod ~/MyRadio]$ grep -rn "header('Loc" .
./src/Classes/MyRadio/CoreUtils.php:215:        header('Location: ' . self::makeURL($module, $action, $params));
./src/Classes/MyRadio/CoreUtils.php:770:        header('Location: ' . $_SERVER['HTTP_REFERER'] . (strstr($_SERVER['HTTP_REFERER'], '?') !== false ? '&' : '?') . 'message=' . base64_encode($message));
./src/Controllers/brokerVersion.php:28:    header('Location: ?service='.$_REQUEST['svc_name']);
./src/PublicAPI/index.php:45:    header('Location: rtfm');
./src/Views/MyRadio/back.php:2:header('Location: '.$_SERVER['HTTP_REFERER']);
```

obviously the first 2 are necessary, but i wasn't sure about the others, as they seemed significantly different to the rest of them

There are also some changed lines which I wasn't sure of either