webapp: fix inverter "add" and "save order" button positions

the source tells us that the buttons are supposed to be on the right of
tha card, but the CSS broke at some point.

webapp/src/views/InverterAdminView.vue

@@ -20,8 +20,8 @@
                         required
                     />
                 </div>
-                <div class="ml-auto text-right">
-                    <button type="submit" class="btn btn-primary my-2">
+                <div class="d-flex my-3">
+                    <button type="submit" class="btn btn-primary ms-auto">
                         {{ $t('inverteradmin.Add') }}
                     </button>
                 </div>
@@ -81,8 +81,8 @@
                     </tbody>
                 </table>
             </div>
-            <div class="ml-auto text-right">
-                <button class="btn btn-primary my-2" @click="onSaveOrder()">
+            <div class="d-flex mt-1 mb-3">
+                <button class="btn btn-primary ms-auto" @click="onSaveOrder()">
                     {{ $t('inverteradmin.SaveOrder') }}
                 </button>
             </div>