Kicks are now temp bans

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