message: Fix grouping in Activity blocks popup
diff: <ItemsControl.ItemTemplate>
  <DataTemplate>
  <Rectangle Width="20" Height="{Binding Height}"
  + MinHeight="6"
  + MaxHeight="50"
  RadiusX="{Binding Height, Converter={StaticResource HeightToRadiusConverter}, ConverterParameter='RadiusX'}"
  RadiusY="{Binding Height, Converter={StaticResource HeightToRadiusConverter}, ConverterParameter='RadiusY'}"
  Panel.ZIndex="1"
  </Style>
  </ItemsControl.ItemContainerStyle>
  </ItemsControl>
  - <Popup DataContext="{Binding SelectedActivityBlock}" Grid.Row="1" Grid.Column="4"
  + <Popup DataContext="{Binding SelectedActivityBlock}"
  + Grid.Row="1" Grid.Column="4"
  Placement="Left"
  StaysOpen="False"
  HorizontalOffset="-5"
  - Name="ActivityBlockPopup"
  - MaxWidth="170">
  - <Border BorderBrush="{DynamicResource Toggl.PopupBorderBrush}" BorderThickness="1">
  + MaxWidth="270"
  + Name="ActivityBlockPopup">
  + <Border BorderBrush="{DynamicResource Toggl.PopupBorderBrush}" BorderThickness="1" Focusable="False">
  <Border.Effect>
  <DropShadowEffect ShadowDepth="1" BlurRadius="4" Direction="270" Opacity="0.2" Color="Black" />
  </Border.Effect>
  