addAccount method
Implementation
Future<void> addAccount(Map acc) async {
final pairs = _storage.keyPairs.val.toList();
// remove duplicated account and add a new one
pairs.retainWhere((e) => e['pubKey'] != acc['pubKey']);
pairs.add(acc);
_storage.keyPairs.val = pairs;
setCurrentPubKey(acc['pubKey']);
}