Ban improvements

- Save a note of the username, not just the reason.
- Allow setting a mask with the `banip` command.
- Make ban.txt's formatting a lot more sane. Username and reason are stored in quotes. The mask uses the same formatting as actual CDIR.
- Keep track of if we tried to load ban.txt. If it wasn't, then don't save over it with a blank file.
- Disallow quotes in player names, as it makes player name detection in console more annoying, and saving username in files scary.

# Conflicts:
#	src/d_clisrv.c
#	src/d_netcmd.c
#	src/i_tcp.c