Improve game time and wall clock display

1. Counting backward for gametimedisplay = 1 and forward for 2. The setting
added to HUD menu.
2. Changed name from clockdisplay to gimetimedisplay, in order to
distinguish clocks with system time and game time.
3. Added to wall clock options with UTC/GMT time and 12h format.

DOCREF clockcount clockdisplay gametimedisplay

source/src/clientgame.cpp

@@ -975,7 +975,7 @@ void timeupdate(int milliscur, int millismax)
     }
     else
     {
-        extern int clockdisplay; // only output to console if no hud-clock is being shown
+        extern int gametimedisplay; // only output to console if no hud-clock with game time is being shown
         int sec = 60 - ( (gametimecurrent + ( lastmillis - lastgametimeupdate ) ) / 1000) % 60;
         if(minutesremaining==1)
         {
@@ -983,7 +983,7 @@ void timeupdate(int milliscur, int millismax)
             hudoutf("%s1 minute left!", sec==60 ? "" : "less than ");
             exechook(HOOK_SP_MP, "onLastMin", "");
         }
-        else if(!clockdisplay) conoutf("time remaining: %d minutes", minutesremaining);
+        else if(!gametimedisplay) conoutf("time remaining: %d minutes", minutesremaining);
         else clientlogf("time remaining: %d minutes", minutesremaining);
     }
 }