center single/multiple buttons in settings dialog

app/settings/settingsdialog/settingsdialog.ui

@@ -40,6 +40,8 @@
         <layout class="QVBoxLayout" name="verticalLayout_3">
          <item>
           <layout class="QHBoxLayout" name="horizontalLayout_3">
+           <item>
+            <layout class="QHBoxLayout" name="horizontalLayout_5">
              <item>
               <spacer name="horizontalSpacer">
                <property name="orientation">
@@ -72,6 +74,10 @@
                </property>
               </widget>
              </item>
+            </layout>
+           </item>
+           <item>
+            <layout class="QHBoxLayout" name="horizontalLayout_6">
              <item>
               <widget class="QToolButton" name="multipleToolBtn">
                <property name="toolTip">
@@ -103,6 +109,8 @@
              </item>
             </layout>
            </item>
+          </layout>
+         </item>
          <item>
           <layout class="QHBoxLayout" name="horizontalLayout_2">
            <item>