The server list used hand-numbered saveName%1/server%1 keys and an O(n)
shift loop to delete entries. Store the profiles with beginReadArray and
beginWriteArray instead, and migrate the legacy keys once in the
constructor so existing profiles and saved passwords survive.
SettingsManager::batchWrite no longer disables atomic sync, so a batch is
still written through QSettings' atomic save. Add tests for add, update,
remove, password updates and the legacy migration.
Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
