SelectedAppointments should not be read only.

The appointment objects that have been cleared from the appointment source stay alive.

I have discovered a bug that appears when a RadScheduleView is used with the ScheduleViewStyleSelector to style the appointments and the theme is changed.

Steps to reproduce:

1. Setup a WPF project.
2. Use implicit styles with a theme (e.g. Office_Black).
3. Create a possibility to change the theme on runtime (e.g. to Fluent). (https://docs.telerik.com/devtools/wpf/styling-and-appearance/how-to/styling-apperance-themes-runtime)
4. Create a dialog with a RadScheduleView that uses a custom ScheduleViewStyleSelector as AppointmentStyleSelector. (https://docs.telerik.com/devtools/wpf/controls/radscheduleview/styles-and-templates/appointment-style)
5. Create at least one appointment.
6. Start application.
7. Change theme at runtime.

Result: The "old" appearance of the appointments stays after changing the theme.

Expected behavior: The appearance of the appointments changes according to the new theme.

I have attached a solution with the described behavior and an image of the outcome.

In WeekView, when ShowWeekGroupHeaders is set, templating the GroupHeaders with GroupHeaderContentTemplateSelector lead to a rendering issue (see attached files).

In case I forgot something, here is my GroupHeaderContentTemplateSelector definition : 

    <svcore:GroupHeaderContentTemplateSelector x:Key="_GroupHeaderContentTemplateSelectorKey">
      <svcore:GroupHeaderContentTemplateSelector.HorizontalTemplate>
        <DataTemplate>
          <ContentPresenter MinHeight="16" Margin="4" Content="{Binding FormattedName, Converter={StaticResource UpperCaseStringConverter}}"/>
        </DataTemplate>
      </svcore:GroupHeaderContentTemplateSelector.HorizontalTemplate>
      <svcore:GroupHeaderContentTemplateSelector.VerticalTemplate>
        <DataTemplate>
          <ContentPresenter Margin="4" MinHeight="16" VerticalAlignment="Top" Content="{Binding FormattedName, Converter={StaticResource UpperCaseStringConverter}}">
            <ContentPresenter.LayoutTransform>
              <RotateTransform Angle="-90"/>
            </ContentPresenter.LayoutTransform>
          </ContentPresenter>
        </DataTemplate>
      </svcore:GroupHeaderContentTemplateSelector.VerticalTemplate>
      <svcore:GroupHeaderContentTemplateSelector.HorizontalResourceTemplate>
        <DataTemplate>
          <Border Background="{Binding Name.DBResource.Color, Converter={StaticResource _SharedStringColorToSolidColorBrushConverterKey}}" Height="60" Margin="2">
            <StackPanel Orientation="Vertical" Margin="8">
              <TextBlock Foreground="{Binding Name.DBResource.Color, Converter={StaticResource _SharedBackgroundStringColorToForegroundConverterKey}}" FontSize="16" Margin="0" Text="{Binding Name.DisplayName}" />
              <TextBlock Foreground="{Binding Name.DBResource.Color, Converter={StaticResource _SharedBackgroundStringColorToForegroundConverterKey}}" FontSize="12" Text="{Binding Name.DBResource.Code}" />
            </StackPanel>
          </Border>
        </DataTemplate>
      </svcore:GroupHeaderContentTemplateSelector.HorizontalResourceTemplate>
      <svcore:GroupHeaderContentTemplateSelector.VerticalResourceTemplate>
        <DataTemplate>
          <Border Background="{Binding Name.DBResource.Color, Converter={StaticResource _SharedStringColorToSolidColorBrushConverterKey}}" Width="140" Margin="2">
            <StackPanel Margin="8">
              <TextBlock Foreground="{Binding Name.DBResource.Color, Converter={StaticResource _SharedBackgroundStringColorToForegroundConverterKey}}" FontSize="16" Margin="-2 3 0 5"  Text="{Binding Name.DisplayName}" />
              <TextBlock Foreground="{Binding Name.DBResource.Color, Converter={StaticResource _SharedBackgroundStringColorToForegroundConverterKey}}" FontSize="12" Text="{Binding Name.DBResource.Code}" />
            </StackPanel>
          </Border>
        </DataTemplate>
      </svcore:GroupHeaderContentTemplateSelector.VerticalResourceTemplate>
    </svcore:GroupHeaderContentTemplateSelector>

It happens when the DefaultDialogResult is set to true.

hi,
I have use telerik scheduler for wpf platforms and in timelineview if I add timeslots in 11:00 to 3:00 pm then its shows in scheduler from 11:00 to 2:59 but not shows 3:00.
how 3:00 will also appear on the scheduler.