Finished implementing basic quest functionality.

Updated CMSG_QUESTGIVER_CHOOSE_REWARD structure and opcode.
Updated CMSG_QUESTGIVER_COMPLETE_QUEST structure and opcode.
Updated CMSG_QUESTGIVER_REQUEST_REWARD structure and opcode.
Updated SMSG_QUESTGIVER_OFFER_REWARD structure and opcode.
Updated SMSG_QUESTGIVER_QUEST_COMPLETE structure and opcode.
Updated SMSG_QUESTGIVER_QUEST_LIST structure and opcode.
Updated SMSG_QUESTGIVER_REQUEST_ITEMS structure and opcode.
A few other misc fixes.