Port to qtkeychain
Accounts data is now stored through qtkeychain. This allows easier deployments on platforms where KWallet is not available or desiderable. qtkeychain's API is less expressive than KWallet's, so this port resulted in a bit more LOCs: * it's not possible to store a QMap, we need to serialize it to QByteArray first. * it's not possible to retrieve the list of stored entries (accounts), so we store an additional entry with the list of all stored accounts.