Add support for different types of ImageSource

[punker76]

Add support for BitmapImage or ImageSource which doesn't come from a Uri, via the existing IconSource property. With this we can use the image extension from https://github.com/MahApps/MahApps.Metro.IconPacks but also many other ways.

<tb:TaskbarIcon
    xmlns:iconPacks="http://metro.mahapps.com/winfx/xaml/iconpacks"
    IconSource="{iconPacks:CooliconsImage Kind=Alarm, Brush=Chartreuse}">
</tb:TaskbarIcon>

Add also support for a FrameworkElement as Icon source with the new property IconFrameworkElementSource.

<Grid>
    <Grid.Resources>
        <Grid x:Key="Icon" HorizontalAlignment="Center" VerticalAlignment="Center">
            <StackPanel Orientation="Horizontal">
                <TextBlock FontFamily="Cascadia Code" Text="4" Foreground="Chartreuse" />
                <TextBlock FontFamily="Cascadia Code" Margin="2 0" Text="2" Foreground="Tomato" />
            </StackPanel>
        </Grid>
    </Grid.Resources>

    <tb:TaskbarIcon
        xmlns:iconPacks="http://metro.mahapps.com/winfx/xaml/iconpacks"
        IconFrameworkElementSource="{StaticResource Icon}"
    </tb:TaskbarIcon>
</Grid>

Most of the source and idea is from @Lakritzator and this PR

• https://bitbucket.org/hardcodet/notifyicon-wpf/pull-requests/11
• https://bitbucket.org/rkrom/notifyicon-wpf/src/master/

Closes #24
Closes #71