Create a single struct for bannednode and bannednodetimelft, and use the matching ban ID inside that struct.

While this commit does not increase the visibility of ban reasons, it makes this possible later.

- 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

Length is determined by the "kicktime" cvar, in minutes. By default, this is set to 10, but I'm willing to adjust this. Only applies to manual kicks (in the future, maybe also name filter kicks).

The timestamp for the unban time is even saved in ban.txt, so long-term temporary bans are completely possible. (I checked, you can attempt to ban someone for up to 1902 years if you really want to.)

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

- Properly call D_SaveBan after remote bans. Bans are no longer saved in the ban command and instead wait for the actual kick to process, since before they were split between the two, which is what caused the discrepancy.

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

-Added a timeout for game state downloading to prevent definitive join freezes in some cases. The timeout has a minimum value of "jointimeout" and gets higher as the game state grows in size
-If the server tries to kick a joiner who is downloading the game state, they will get a timeout instead, because a regular kick would only happen once the game state has been downloaded
-Added a timeout for player ticcmd packets, again to prevent freezes to happen in some cases
-File/game state downloading is now faster, the speed is controlled by the "downloadspeed" cvar, in packets per tic
-The reason is now properly shown when the server refuses connection
-Changed the default values of "nettimeout" to 10 seconds (previously 15) and "maxsend" to 4 MB (previously 1)
-Added a "noticedownload" cvar that displays a message in the server console when someone is downloading a file

This reverts commit 8607f524, reversing
changes made to 11d76a65.

The code in i_net.c doesn't actually seem to be used in SRB2. I was able to compile a build without it, and hosting and joining netgames worked just fine (well, as fine as they can with the current state of the netcode...).

Do we really need to keep it around? If not, I say get rid of it. It seems like useless clutter that is just going to confuse people who are trying to understand the source code.

(no actual SLOC changes)