MapStorage doesn't extend Storage + introduced Transformers

- `MapStorage` doesn't extend `Storage` anymore
- introduced `Transformer` instead of wrapping sub-storages

## Storage

- `FileStorage`
- `MemoryStorage`

## MapStorage

- `MultipleFileStorage`
- `ArrayStorage`

## Transformer

- `JsonEncoder`
- `YamlEncoder`
- `PhpSerializerEncoder`
- `ObjectArrayMapper`
- `AesEncrypter`