Add TNTMode to ONLY_TB

BauSystem_Main/src/de/steamwar/bausystem/commands/CommandTNT.java

@@ -38,6 +38,12 @@ public class CommandTNT implements CommandExecutor, Listener {
 
     private static TNTMode tntMode = TNTMode.OFF;
 
+    static {
+        if (Region.buildAreaEnabled()) {
+            tntMode = TNTMode.ONLY_TB;
+        }
+    }
+
     public static TNTMode getTntMode() {
         return tntMode;
     }