message: wpf: Change scrollbar buttons to one line per click
  Fix scrolling in the WPF control so that clicking the arrow buttons scrolls one line at a time.
diff: <ColumnDefinition Width="Auto"/>
  </Grid.ColumnDefinitions>
  <local:TerminalContainer x:Name="termContainer"/>
  - <ScrollBar x:Name="scrollbar" Scroll="Scrollbar_Scroll" Grid.Column="1" />
  + <ScrollBar x:Name="scrollbar" Scroll="Scrollbar_Scroll" SmallChange="1" Grid.Column="1" />
  </Grid>
  </UserControl>
  