rlp serialization refactor (#4873)

* fixed naming of rlp modules

* RlpStream cleanup

* appending short rlp lists (0...55 bytes) is 25% faster

* RlpStream does not use bytes module, nor trait Stream

* removed unused code from rlp module

* compiling ethcore-util with new rlp serialization

* compiling parity with new rlp serialization

* fixed compiling ethcore-light with new rlp serialization

* fixed compiling ethsync with new rlp serialization

* removed redundant comment, print

* removed redundant double-space

* replace usage of WriteBytesExt with ByteOrder