[Patch 2/4] Network rework: packet writing, sending and cleanups

NetworkPacket.cpp:
* Remove some deprecated functions, we must use streaming interface
* m_data converted from u8* to std::vector<u8>
* Add an exporter to forge packet to Connection object
* implement operator << std::wstring. n
* implement operator << std::string
* dynamic resize when write packet content.
* fix string writing and performances.
* create ServerCommandFactory, used by client to get useful informations about packet processing (sending).
  * Reliability
  * Transmit channel
* Implement putRawString for some ugly char (_INIT packet), and use it.
* Many packet read and write migrated
* Implement oldForgePacket to interface writing with current connection
* fix U8/char/bool writing
* fix string writing and performances.
* add some missing functions
* Use v3s16 read instead of reading x,y,z separately
* Add irr::video::SColor support into packets
* Add some missing handlers
* Add a template function to increase offset
* Throw a serialization error on packet reading (must be improved)

PacketFactories:
* Create ServerCommandFactory, used by client to get useful informations about packet processing (sending).
* Create ClientCommandFactory, used by server to get useful informations about packet processing (sending).

Client.cpp:
* implement NetworkPacket ::Send interface.
* Move packet handlers to a dedicated file
* Remove Client::Send(SharedBuffer)

Server.cpp:
* implement NetworkPacket ::Send interface.
* Rewrite all packets using NetworkPacket
* Move packet handlers to a dedicated file
* Remove Server::Send(SharedBuffer)

ClientIface.cpp:
* Remove sendToAll(SharedBuffer<u8>)

Connection.hpp rework:
* Remove duplicate include
* Remove duplicate negation
* Remove a useless variable
* Improve code performance by using a m_peers_list instead of scanning m_peers map
* Remove Connection::Send(SharedBuffer)
* Fix useafterfree into NetworkPacket Sending
* Remove unused Connection::sendToAll

Test.cpp:
* Remove dead code
* Update tests to use NetworkPackets

Misc:
* add new wrappers to Send packets in client, using NetworkPacket
* Add NetworkPacket methods for Connection
* coding style fix
* dead code since changes cleanup
* Use v3s16 read instead of reading x,y,z separately in some packets
* Use different files to handle packets received by client and server
* Cleanup: Remove useless includes

ok @Zeno-
Tested by @Zeno- @VanessaE and @nerzhul on running servers