Manual AI seats for matches: host toggles empty seats, co-op allies fight heroes

lang/de.lang

@@ -643,6 +643,8 @@ net.side0 = Rot
 net.side2 = Blau
 net.side3 = Grün
 net.side4 = Gelb
+net.ai = KI
+net.ai_off = Aus
 
 # rival masters (free game)
 newgame.difficulty = Gegner

lang/en.lang

@@ -644,6 +644,8 @@ net.side0 = Red
 net.side2 = Blue
 net.side3 = Green
 net.side4 = Yellow
+net.ai = AI
+net.ai_off = Off
 
 # rival masters (free game)
 newgame.difficulty = Opponents