This makes it easier to add checks in handlers, which should improve security over time.
I think this approach is more readable and testable than calling Client#disconnect straight up,
while it also decentralizes the handling.
This commit got way too big...
- Remove deprecated methods for sending packets
- Favor OutPacket & Packet over MaplePacketLittleEndianWriter, LittleEndianWriter, and byte array
- Split up some packet creating methods into separate classes
