change shallow equality, hash to deep one

[Abdktefane]

fixed #233

[clragon]

Rebuilds like this usually shouldnt be that costly. I dont think this change should be implemented. However, the cleanest way would be the following:

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) {
      return true;
    }
    return other is PagingState &&
        listEquals(other.itemList, itemList) &&
        other.error == error &&
        other.nextPageKey == nextPageKey;
  }

[clragon]

closing this as its outdated.