Added hashCode and == operator to all params

I needed this for ScryptParams and decided to add it to all of them.

Only one still has an issue (I placed a TODO): ParametersWithRandom. For this param, I only took the runtimeType of the SecureRandom into account. Otherwise, I'd have to implement hashCodes and equals for all randoms as well, which would cascade in adding them to all block ciphers.

I know runtimeType is not enough. For now, I clearly documented this drawback so I hope it's ok.

I had to add dependency for package:collection to pubspec.