Reorganize net.secloud.core.utils package

Rename classes

BinaryReader -> BinaryStreamReader
BinaryWriter -> BinaryStreamWriter

and make them extend the new traits StreamReader and StreamWriter. The
implicit conversions from InputStream and OutputStream to the
corrosponding reader and write class are now methods of the package
object.

Remove RichStream and move the single needed method pipeTo into the
StreamUtils class as pipeStream method.
Make BlockInputStream, BlockOutputStream private

Instead add methods StreamReader.readStream and StreamWriter.writeStream
to allow reading and writing of inner streams using the BlockInputStream
and BlockOutputStream.
Make NullEncryptionSpec serialization independent
Remove duplicated code from tests