Include Elements Xaml - Uno

Update the StackPanel to remove the HorizontalAlignment property, as we'll be centering each of the nested elements individually.
xml
```
<StackPanel VerticalAlignment="Center">
```

Update the Image element to center it horizontally and add a margin.

xml

<Image Width="150"
       Height="150"
       Margin="12"
       HorizontalAlignment="Center"
       Source="Assets/logo.png" />

Add a TextBox to allow the user to enter the step size.

xml

<TextBox Margin="12"
         HorizontalAlignment="Center"
         PlaceholderText="Step Size"
         Text="1"
         TextAlignment="Center" />

Add a TextBlock to display the current counter value.

xml

<TextBlock Margin="12"
           HorizontalAlignment="Center"
           TextAlignment="Center"
           Text="Counter: 1" />

Add a Button to increment the counter.

xml

<Button Margin="12"
        HorizontalAlignment="Center"
        Content="Increment Counter by Step Size" />