Maps: Remembering last active map on map save only

The last active map is remembered only if the map is saved. This stops
unnecessary writes into RPG_RT.lmt. This change should fix issue #129.

src/ui/main_window.cpp

@@ -1057,12 +1057,6 @@ void MainWindow::on_treeMap_currentItemChanged(QTreeWidgetItem* current, QTreeWi
 		ui->actionMapDelete->setEnabled(false);
 		return;
 	}
-	int id = current->data(1, Qt::DisplayRole).toInt();
-	ui->actionMapCopy->setEnabled(id != 0);
-	ui->actionMapDelete->setEnabled(id != 0);
-	if (id != 0) {
-		core().project()->treeMap().active_node = id;
-	}
 }
 
 void MainWindow::on_actionMapCopy_triggered()

src/ui/map/map_scene.cpp

@@ -364,6 +364,8 @@ void MapScene::Save(bool properties_changed)
 			treeMap.maps[i] = n_mapInfo; //Apply info changes
 			break;
 		}
+	// Remember last active map
+	treeMap.active_node = n_mapInfo.ID;
 	// FIXME: ProjectData.Project is Const
 	core().project()->saveTreeMap();
 	QString file = QString("Map%1.emu")