Command should expose IconPath, not IconSource

[carlos-zamora]

CommandPalette data binds itself to the IconSource of Command. Command should instead operate more like Profile in that it only exposes the IconPath.

CommandPalette can still be bound to the command's icon by using a converter like this:

            <local:HasNestedCommandsVisibilityConverter x:Key="HasNestedCommandsVisibilityConverter"/>

or

                                    Visibility="{x:Bind HasNestedCommands,
                                                 Mode=OneWay,
                                                 Converter={StaticResource HasNestedCommandsVisibilityConverter}}"

(also see CommandKeyChordVisibilityConverter)

This'll also be very useful for Profile too because...

1. Profile icons will now be able to be set to non-path images (i.e. SegoeUI icons, emoji, etc.)
2. Settings UI will need a similar kind of data binding in the very near future.