Network Layer 7 rework (Packet handling)

* Move networkcode to a dedicated directory
* Rename clientserver.h to network/networkprotocol.h (Better name) and sanitize some includes
* Create object NetworkPacket
  * It stores command (opcode) and data separated
  * It also stores peer_id
  * Data reading can be done by using a streaming interface
* Change packet routing analysis
  * Remove old conditional analysis
  * Now uses function pointed analysis and add connection state ({Client,Server}::handlers)
  * Connection state permit to categorize condition to handle before analyze packets
  * Create a handler for depreciated messages, instead of duplicating code

src/CMakeLists.txt

@@ -429,6 +429,9 @@ set(common_SRCS
 	version.cpp
 	voxel.cpp
 	voxelalgorithms.cpp
+	network/networkpacket.cpp
+	network/serveropcodes.cpp
+	network/toserverpacket.cpp
 	${JTHREAD_SRCS}
 	${common_SCRIPT_SRCS}
 	${UTIL_SRCS}
@@ -491,6 +494,8 @@ set(minetest_SRCS
 	sky.cpp
 	tile.cpp
 	wieldmesh.cpp
+	network/clientopcodes.cpp
+	network/toclientpacket.cpp
 	${minetest_SCRIPT_SRCS}
 )
 list(SORT minetest_SRCS)