Updated docs. Minior fixes.

Added flag on some timers so we are sure they are killed on map change.
Added stop event on health regeneration timer when applying classes, if the class has no regeneration.
Cvar zr_classes_default_admin is now replaced by admin-only classes. Old cvar is zr_classes_default_admin_mode.

src/zr/playerclasses/apply.inc

@@ -325,6 +325,8 @@ bool:ClassApplyHealthRegen(client, classindex, cachetype = ZR_CLASS_CACHE_PLAYER
     }
     else
     {
+        // Make sure old timers are stopped.
+        ClassHealthRegenStop(client);
         return false;
     }
 }