Remove TODO comment and add correct handling for client with exception sockets.

Also add TODO for sending data to the client if we have any left before
disconnecting.
Replace constant 8 with const variable for representing the BB header length.
Remove TODO and unnecessary variable.
Move login_process_packet into login.cc and define new packet types.

Attempting to clean up login_server.cc since all of the functionality
for the login, character, and ship servers is in one file.
Move server and database config into global structs.

They may still be global, but at least now they're more organized
and can be passed around more cleanly. This commit is huge and involves
a lot of small changes that fix errors caused by this transition including
removing dead code and changing references.
Move mysql database connection into mysql_config struct.

All accompanying changes fix errors that came about as a result
of this reolcation.
Replace start_encryption with limit_connections.

This better indicates its use and it's now actually called again.
Remove unused variables from main in login_server.cc.