Replaced all references to chunk->players and chunk->NPCs with
chunk->entities and all instances of the old NPCClass enum with
EntityType.
The server compiles but will not yet run properly.
This change subtly broke the poll() loop when a connection was removed,
because erasing an entry from fds would invalidate the iterator that
was still being used.
This reverts commit ec67cc6527.
CNProtocol, CNShared, CNStructs and Defines are now in core/.
CNLoginServer, CNShardServer and Monitor are now in servers/.
core/Core.hpp wraps all the core headers except for CNShared.hpp.
Defines.cpp has been renamed to Packets.cpp, and so has its
corresponding namespace, but not the header file. This is in preparation
for upcoming changes.
