store method
stores the current user to the device
Implementation
Future store() async {
await _storage.write(key: _username_store, value: name);
await _storage.write(key: _userpass_store, value: pass);
(await _prefs).setString(_full_name_store, full_name ?? 'noname');
(await _prefs).setString(_full_surname_store, full_surname ?? 'noname');
}